Four-wave Mixing Efficiency Research Articles

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.

Phase-sensitive amplification of a QPSK signal using a dispersion engineered silicon-graphene oxide hybrid waveguide.

We numerically investigate phase-sensitive amplification of a quadrature phase shift keying (QPSK) signal in a 35 µm dispersion engineered silicon-graphene oxide hybrid waveguide. The four-wave mixing efficiency is effectively enhanced by exploiting the ultrahigh Kerr nonlinearity and low loss of graphene oxide in the ultrawide wavelength range. A new structure of dispersion flat silicon-graphene oxide hybrid waveguide is proposed and used to achieve the phase regeneration of a QPSK signal using a dual-conjugated-pump degenerate scheme. The phase-dependent gain and phase-to-phase transfer functions are calculated to analyze the properties of a phase-sensitive amplifier (PSA). The constellation diagrams of the QPSK signal and the error vector magnitude are used to assess the regeneration capacity. The simulation results show that the proposed PSA with a good phase noise squeezing capability has potential applications in all-optical signal processing.

Correlated photon pair generation in ultra-silicon-rich nitride waveguide

Correlated photon pair generation is demonstrated using ultra-silicon-rich nitride waveguides. Waveguides with a length of 10 mm, nonlinear parameter of 530 W−1/m and anomalous dispersion are used to achieve spontaneous four-wave mixing. A generated coincidence rate of 2.40×105 counts per second is achieved, and derived from a measured coincidence rate of ∼1 counts per second at the maximum coupled power of 5 mW, in line with the expected quadratic dependence of spontaneous four-wave mixing efficiency on power. Utilizing picosecond pulses as the pump, we achieve a measured coincidence rate of up to 1.8 counts per second, resulting in a generated coincidence rate of 2.20×10−2 counts per pulse at the maximum peak power of 8.33 W. 2.3 times larger coincidence-to-accidental ratio is also obtained using a pulsed pump compared to that achieved with a continuous-wave pump. Further enhancements via the use of ring resonators may be adopted.

Improving FWM efficiency in bi-directional ultra DWDM-PON networking centered light source by using PMD emulator

The optical networks provides a high performance data networking and secured way to communicate. New generation optical networks demands high input power and low channel spacing in Wavelength-Division Multiplexing (WDM). Using WDM can lead to some nonlinearities in the system such as Four Wave Mixing (FWM). FWM is a phenomena in which two optical pulses are converted into four pluses after traveling in optical fiber. In this paper Polarization Mode Dispersion (PMD) is used by applying PMD emulator at input to suppress FWM. To analyse the effect of PMD a Dense Wavelength-Division Multiplexing-passive optical network (DWDM-PON) is used with centerlized source over the transemission distance longer than 50 km. System’s performance is carried out on the basis of Q factor, optical signal to noise ratio (OSNR), bit error rate (BER), received power and FWM efficiency. Exhaustive sets of simulations are carried out in “Optisystem” on a eight channel system having 25 GHz spacing, operating at 5 Gbps. Results show 7 dB and 5 dB of improved FWM efficiency in downlink and uplink respectively.

Control of the nonlinear response of bulk GaAs induced by long-wavelength infrared pulses.

The nonlinear optical response of GaAs is studied using extremely nonresonant 10 μm laser pulses with peak intensities greater than 2 GW/cm 2. We observe over an order of magnitude enhancement in the four-wave mixing efficiency by decreasing the CO 2 laser beat-wave frequency. This enhancement is attributed to currents of photoexcited unbound carriers modulated at the beat frequency, confirmed by measurements of nonlinear absorption at this long wavelength as well as a fully microscopic analysis of the excitation dynamics. Modeling of such nonperturbative semiconductor-laser interactions predicts that further decreasing the beat frequency can increase the nonlinear response and allow for its control over two orders of magnitude.

Ultra-low power all-optical wavelength conversion of high-speed data signals in high-confinement AlGaAs-on-insulator microresonators

Wavelength conversion technology is imperative for the future high-speed all-optical network. Nonlinear four-wave mixing (FWM) has been used to demonstrate such functionality in various integrated platforms because of their potential for the realization of a chip-scale, fully integrated wavelength converter. Until now, waveguide-based wavelength conversion on a chip requires a pump power beyond the reach of available on-chip lasers. Although high-quality factor (Q) microresonators can be utilized to enhance the FWM efficiency, their narrow resonance linewidths severely limit the maximal data rate in wavelength conversion. In this work, combining the ultrahigh effective nonlinearity from a high-confinement aluminum gallium arsenide waveguide and field enhancement from a microring resonator with a broad resonance linewidth, we realize all-optical wavelength conversion of a 10-Gbaud data signal by using a pump power, for the first time, at a submilliwatt level. With such a low operation power requirement, a fully integrated high-speed wavelength converter is envisioned for the future all-optical network. The waveguide cross-sectional dimension is engineered in a submicron scale to enhance the light confinement, which pushes the device effective nonlinearity to 720 W−1 m−1 while maintaining a broad operation bandwidth covering the telecom S-, C-, and L-bands. Moreover, we demonstrate that a single microring resonator is capable of handling a high-speed data signal at a baud rate up to 40 Gbit/s. All the wavelength conversion experiments are validated with bit-error rate measurements.

Characterize and optimize the four-wave mixing in dual-interferometer coupled silicon microrings**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0303700), the National Natural Science Foundation of China (Grant Nos. 61632021, 11627810, 11690031, and 11621091), and Open Funds from the State Key Laboratory of High Performance Computing of China (HPCL, National University of Defense Technology).

By designing and fabricating a series of dual-interferometer coupled silicon microrings, the coupling condition of the pump, signal, and idler beams can be engineered independently and then we carried out both the continuous-wave and pulse pumped four-wave mixing experiments to verify the dependence of conversion efficiency on the coupling conditions of the four interacting beams, respectively. Under the continuous-wave pump, the four-wave mixing efficiency gets maximized when both the pump and signal/idler beams are closely operated at the critical coupling point, while for the pulse pump case, the efficiency can be enhanced greatly when the pump and converted idler beams are all overcoupled. These experiment results agree well with our theoretical calculations. Our design provides a platform for explicitly characterizing the four-wave mixing under different pumping conditions, and offers a method to optimize the four-wave mixing, which will facilitate the development of on-chip all-optical signal processing with a higher efficiency or reduced pump power.

High-efficiency four-wave mixing beyond pure electromagnetically induced transparency treatment.

We present a theoretical study of high-efficiency four-wave mixing (FWM) sum-frequency generation beyond a pure electromagnetically induced transparency (EIT) technique in a five-level atomic system. In our FWM scheme, with the assistance of two Λ-type subsystems utilized to create EIT and Autler-Townes splitting (ATS), a synergetic mechanism of EIT and ATS, or a dual-ATS mechanism is induced. These novel mechanisms can have a significant impact on the FWM process in the optically thick medium, and the FWM efficiency can be several orders of magnitude larger than that obtained from the pure EIT method. This Letter opens up a new perspective for exploring enhanced quantum nonlinear optical phenomena.

Generation Efficiency of Fiber Four-Wave Mixing for Phase-Shift Keying Signal Light

Generation Efficiency of Fiber Four-Wave Mixing for Phase-Shift Keying Signal Light

FWM Reduction Using Different Modulation Techniques and Optical Filters in DWDM Optical Communication Systems: A Comparative Study

Next-generation optical communication networks require high input power and more number of channels at low spacing. This can be achieved using dense wavelength division multiplexing (DWDM). However, increasing the number of channels and decreasing channel spacing can enhance fiber nonlinearities, especially the four-wave mixing (FWM). In this paper, different modulation techniques and optical filters are considered and investigated to reduce the FWM effect in DWDM optical communication systems. System performance is evaluated through its quality factor (Q-factor), optical signal-to-noise ratio, optical received power and FWM efficiency. All used techniques have shown a reduction in FWM efficiency. The highest reduction in FWM efficiency is 25 dB and is reported while using modified Duobinary modulation with an increase of 2 in the Q-factor. A comparative study is carried out for the different techniques at 10–20 Gbps bit rate. All simulations are performed through Optisystem.

Circulator-free on-chip bidirectional four-wave mixing.

On-chip bidirectional four-wave mixing (FWM), which may meet the rapidly increasing demands on integration level and system versatility, has never been implemented for the lack of competent on-chip optical circulators that are indispensable for separating the bidirectional channels. In this scenario, we first propose and demonstrate a circulator-free scheme that fully utilizes the inherent clockwise and counter-clockwise transmission natural of an add-drop microring resonator to implement on-chip bidirectional FWM. It should be noted that the proposed scheme additionally provides a universal solution for multichannel nonlinear operations and the related applications, with the advantages of compact structure and low crosstalk. The implementation for multimode channels is investigated for demonstration, as the mode division multiplexing technique is of particular interest in integrated optoelectronics and the resonance-enhanced nonlinear structure with superior dimension compared to straight waveguides has never been implemented for a multimode case. The experimental results exhibit that the FWM efficiencies of the two-mode channels are -26.78 and -28.69 dB, respectively, and the crosstalk is lower than -35 dB.

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.

Mid-infrared nonlinear silicon hybrid waveguide with high figure of merit

Mid-infrared (MIR) integrated waveguides with strong local field enhancement and relatively low loss have shown their potential in nonlinear optical applications. We present a novel highly nonlinear silicon hybrid waveguide by setting an insulator-metal-insulator structure with [2-[4-(dimethylamino)phenyl]-3-([4-(dimethylamino)phenyl]ethynyl)buta-1,3-diene-1,1,4,4-tetracarbonitrile] (DDMEBT) and silver materials into the silicon slot. The mode field is strongly confined in the DDMEBT layers via the surface plasmon polariton effect. Two rectangular silicon nanobridges are used to further confine the optical field and reduce the loss simultaneously. The waveguide dimensions are optimized to obtain a figure of merit as high as 0.55 at 2.1 μm and a zero-dispersion wavelength of 2.06 μm. In a 6.6-mm-long waveguide, a maximum four-wave mixing efficiency of −6.65 dB and a bandwidth of 512 nm (1.894–2.406 μm) can be simultaneously obtained, pumped by a 2.104-μm source with a power of only 500 mW. Our designed waveguide exhibits excellent overall performance for nonlinear optical applications such as all-optical signal processing in the MIR band.

All-fiber frequency-resolved optical gating pulse characterization from chalcogenide glass.

We report, to the best of our knowledge, the first all-fiber frequency-resolved optical gating device from nonlinear processing in chalcogenide glass. The strong four-wave mixing efficiency of an 11cm long chalcogenide microwire enables a high sensitivity characterization of pulses in the 2μm wavelength band. The amplitude and phase of chirped and unchirped picosecond pulses are accurately characterized with a high sensitivity of 0.16 mW2.

High-precision two-dimensional atom localization from four-wave mixing in a double-Λ four-level atomic system

We propose a scheme for high-precision two-dimensional (2D) atom localization via the four-wave mixing (FWM) in a four-level double- atomic system. Due to the position-dependent atom-field interaction, the 2D position information of the atoms can be directly determined by the measurement of the normalized light intensity of output FWM-generated field. We further show that, when the position-dependent generated FWM field has become sufficiently intense, efficient back-coupling to the FWM generating state becomes important. This back-coupling pathway leads to competitive multiphoton destructive interference of the FWM generating state by three supplied and one internally generated fields. We find that the precision of 2D atom localization can be improved significantly by the multiphoton destructive interference and depends sensitively on the frequency detunings and the pump field intensity. Interestingly enough, we show that adjusting the frequency detunings and the pump field intensity can modify significantly the FWM efficiency, and consequently lead to a redistribution of the atoms. As a result, the atom can be localized in one of four quadrants with holding the precision of atom localization.

Phase control of highly efficient four-wave mixing in a six-level tripod atomic system.

We investigate theoretically an enhancement of four-wave mixing (FWM) process in phase-dependent double electromagnetically induced transparency (EIT) six-level atomic media. It is shown, owing to the multiphoton destructive interference, that the conversion efficiency of FWM can be enhanced by manipulating the relative phase of the applied fields in this ultraslow propagation regime. Moreover, we also find that the conversion efficiency is amplified with the presence of the microwave field in comparison with the previous six-level scheme [Phys. Rev. A76, 043809 (2007)PLRAAN1050-294710.1103/PhysRevA.76.043809].

Influence of the frequency detuning on the four-wave mixing efficiency in three-level system coupled by standing-wave

In a Λ-type three-level atomic system coupled by an off-resonant standing-wave, the reflected four-wave mixing (FWM) spectrum is studied. It shows that the maximum reflection efficiency occurs when both of the coupling and probe fields are tuned off resonances from the atomic transitions. The essence of enhanced reflection is that the nonlinear efficiency of the FWM based on coherent atoms is improved due to the significant reduction of phase mismatch. The theoretical analysis shows good agreement with the experimental results. Furthermore, the influence of the atomic number density on the coupling frequency detuning of the optimum reflection efficiency and the linewidth are also investigated.

Improved third-order nonlinear effect in graphene based on bound states in the continuum

The scattering matrix theory has been developed to calculate the third-order nonlinear effect in sphere-graphene-slab structures. By designing structural parameters, we have demonstrated that the incident electromagnetic wave can be well confined in the graphene in these structures due to the formation of a bound state in the continuum (BIC) of radiation modes. Based on such a bound state, third-harmonic (TH) generation and four-wave mixing (FWM) have been studied. It is found that the efficiency of TH generation in monolayer graphene can be enhanced about 7 orders of magnitude. It is interesting that we can design structure parameters to make all beams (the pump beam, probe beam, and generated FWM signal) be BICs at the same time. In such a case, the efficiency of FWM in monolayer graphene can be enhanced about 9 orders of magnitude. Both the TH and FWM signals are sensitive to the wavelength, and possess high Q factors, which exhibit very good monochromaticity. By taking suitable BICs, the selective generation of TH and FWM signals for S- and P-polarized waves can also be realized, which is beneficial for the design of optical devices.

Larger enhancement in four-wave mixing from graphene embedded in one-dimensional photonic crystals

We demonstrate theoretically that the efficiency of four-wave mixing (FWM) can be enhanced by more than several orders in monolayer graphene by inserting it in a properly designed photonic crystal (PC). Two kinds of cases are considered. One is monolayer graphene embedded in defect PC, and the other is a stack of monolayer graphene in a dielectric multilayer structure. It is found that a larger enhancement of the efficiency in the FWM from the monolayer graphene can be obtained in two cases. Such an effective enhancement utilizes the improved field localization within the defect state or at the band-edge state. Due to the presence of a feedback mechanism at each interface of the multilayer, we demonstrate that the tunable phase conjugation by an external voltage can be effectively generated when only one pump wave is used.

Power Fluctuations of Intermodal Four-Wave Mixing in Few-Mode Fibers

We demonstrate the full bandwidth measurement of the intermodal four-wave mixing efficiency for a 4.7-km three-spatial-mode few-mode fiber. Large fluctuations of intermodal four-wave mixing between the LP $_{01}$ and LP $_{11}$ modes are experimentally observed. These fluctuations exhibit a strong wavelength dependence that can be persistent in time. The fluctuations are also shown to display some polarization dependence.