Broadband Bright Biphotons From Periodically Poled Brillouin Zone Folding Metasurface

Phase matching must be performed to realize four-wave mixing (FWM) in a silicon waveguide, which is challenging when a signal wavelength is highly deviated from an idler wavelength. To solve this problem, quasi-phase-matching (QPM) based on grating-assisted directional coupling (GADC) in a hybrid structure is theoretically investigated. The proposed system consists of a silicon strip with periodic width modulation as the grating and a silicon nitride strip that is vertically aligned to the silicon strip. GADC occurs between the TE_S mode (mainly confined in the silicon strip) and TE_N mode (mainly confined in the silicon nitride strip) at an idler wavelength. This phenomenon compensates for the phase mismatch occurring in FWM among the TE_S modes at the pump, signal, and idler wavelengths. Results of analysis of the hybrid structure show that the TE_S and TE_N modes at an idler wavelength of 2.1177 μm are efficiently generated with the TE_S modes at a pump wavelength of 1.58 μm and signal wavelength of 1.2601 μm. Moreover, the signal TE_S mode can be efficiently implemented with the pump TE_S mode and idler TE_N mode. Owing to the GADC characteristics, the conversion bandwidth of the signal is 0.8 nm; however, the signal wavelength can be thermally tuned, with a temperature change of 50 °C corresponding to a signal wavelength change of 3.6 nm. The hybrid structure with the GADC-based QPM can be used to generate and detect mid-infrared light with well-developed O-band and L-band devices.

This article shows a dual-frequency OPO with multi-grating (28.5-31.5 μm) periodically poled MgO:LiNbO₃ (MgO:PPLN) pumped by a dual-frequency continuous wave at 1.064 μm. The wavelengths of idler and signal varying versus temperature at different periods of inverted domains were numerical simulated. It proves that as the temperature rises, or as the poling period increases, the idler wavelength shortens and signal wavelength lengthens. The pump is a 30 W dual-frequency fiber laser MOPA with beat note frequency varying from 125 MHz to 175 MHz. The pump threshold of the bow-tie ring cavity OPO was 3 W. An average dual-frequency idler output power of 2.6 W was obtained when the pump power was 17.2 W at 45 °C. The idler wavelength was 3.4 μm when the poling period was 30.5 μm. The idler wavelength could be tuned from 2.9 μm to 3.9 μm by changing the temperature and the poling period, and the beat note frequency was proved to be equal to that of the pump.

By utilizing the extended phase-matching (EPM) method, we investigate the generation of single photons with high spectral-purity in a magnesium-doped periodically-poled lithium niobate (MgO:PPLN) crystal via the spontaneous parametric down-conversion (SPDC) process. By adjusting the temperature and pump wavelength, the wavelength of the single photons can be tuned from telecom to mid-infrared (MIR) wavelengths, for which the spectral-purity can be above 0.95 with high transmission filters. In experiments, we engineer a MgO:PPLN with poling period of 20.35 μm which emits the EPM photon pair centered at 1496.6 nm and 1644.0 nm and carry out the joint spectral intensity (JSI) and Glauber’s second-order self-correlation measurements to characterize the spectral purity. The results are in good agreement with the numerical simulations. Our work may provide a valuable approach for the generation of spectrally pure single photons at a wide range of wavelengths which is competent for various photonic quantum technologies.

We propose the idea of using a grating structure for solving the problem of the incomplete quasi-phase matching (QPM) period and demonstrate the simulation results of phase compensation in achieving efficient round-trip optical parametric oscillation in periodically poled LiNbO/sub 3/ (PPLN). The layout of a monolithic optical parametric oscillator (OPO) with two surface gratings at both ends is shown. The two gratings are chirped to guarantee that their phase variations over the Bragg reflection windows are larger than 2/spl pi/. One of them has a length of 1 mm and the other has a length of 0.8 mm. The pump input is applied from the long grating side and the signal output is obtained from the short grating side. The whole PPLN length is 5 mm. For our numerical study, we consider the pump wavelength at 1064 nm and signal wavelength at 1550 nm. The idler wavelength is hence at 3.393 /spl mu/m. The corresponding QPM period of PPLN is 29.6 /spl mu/m. The central grating period is 361.83 nm, which corresponds to the Bragg wavelength 1550 nm. To obtain numerical results, we solved the coupled equations for the forward and backward pump complex amplitudes, the forward and backward signal complex amplitudes, and the forward and backward idler complex amplitudes.

The influence of the core diameter and pump wavelength on the phase-matching conditions when different signal vector beams are injected is analyzed numerically in a suspended-core ${{\rm As}_2}{{\rm Se}_3}$As2Se3 microstructured optical fiber (MOF). The idler wavelengths satisfying the phase-matching conditions with different signal vector beams can reach wavelengths of 4.8–5.9 µm in the ${{\rm As}_2}{{\rm Se}_3}$As2Se3 MOFs with different core diameters. By changing the signal vector mode field and adjusting the corresponding signal wavelength, the idler wavelength can be tuned in 754.8 nm from 4.9182 to 5.6730 µm with the pump wavelength changing from 2.80 to 2.90 µm. The influence on signal gain and the idler conversion efficiency is calculated in the ${{\rm As}_2}{{\rm Se}_3}$As2Se3 MOFs with different lengths when injecting different signal vector beams. The peak gain of signal and idler conversion efficiency can reach $\sim{28}\,\, {\rm dB}$∼28dB and $\sim{24}\% $∼24%, respectively, when the different signal vector beams are injected. The simulated results demonstrate that the optical parametric oscillation with wavelengths longer than 5 µm can be realized in chalcogenide fibers with signal vector beam injection.

Layered two-dimensional (2D) materials interact primarily via van der Waals (vdW) bonding, which has created opportunities for heterostructures that are not constrained by epitaxial lattice matching [1]. However, since any passivated surface interacts with another via non-covalent forces, vdW heterostructures are not limited to 2D materials alone. In particular, 2D materials can be integrated with a diverse range of other materials, including those of different dimensionality, to form mixed-dimensional vdW heterostructures [2]. Furthermore, chemical functionalization allows tailoring of the properties of 2D materials and the degree of coupling across heterointerfaces [3]. In this talk, the prospects of mixed-dimensional heterostructures for quantum photonic science and technology will be discussed with a focus on how chemical functionalization can manipulate and enhance single-photon emission in strained 2D transition metal dichalcogenides [4]. In addition to technological implications, this talk will explore fundamental issues including band alignment, doping, trap states, and charge/energy transfer across heterointerfaces.[1] D. Lam, et al., ACS Nano, 16, 7144 (2022).[2] M. I. B. Utama, et al., MRS Bulletin, 48, 905 (2023).[3] S. H. Amsterdam, et al., J. Am. Chem. Soc., 143, 17153 (2021).[4] M. I. B. Utama, et al., Nature Communications, 14, 2193 (2023).

We investigate the use of nanocrystal quantum dots as a quantum bus element for preparing various quantum resources for use in photonic quantum technologies. Using the Stark-tuning property of nanocrystal quantum dots as well as the biexciton transition, we demonstrate a photonic controlled-NOT (CNOT) interaction between two logical photonic qubits comprising two cavity field modes each. We find the CNOT interaction to be a robust generator of photonic Bell states, even with relatively large biexciton losses. These results are discussed in light of the current state of the art of both microcavity fabrication and recent advances in nanocrystal quantum dot technology. Overall, we find that such a scheme should be feasible in the near future with appropriate refinements to both nanocrystal fabrication technology and microcavity design. Such a gate could serve as an active element in photonic-based quantum technologies.

We investigate the use of nanocrystal quantum dots as a versatile quantum bus element for preparing various quantum resources for use in photonic quantum technologies. The ability to Stark tune nanocrystal quantum dots allows an important degree of control over the cavity QED interaction. Using this property along with the bi-exciton transition, we demonstrate a photonic CNOT interaction between two logical photonic qubits comprising two cavity field modes each. We find the CNOT interaction to be a robust generator of photonic Bell states, even with relatively large bi-exciton losses. These results are discussed in light of the current state-of-the-art of both microcavity fabrication and recent advances in nanocrystal quantum dot technology. Overall, we find that such a scheme should be feasible in the near future with appropriate refinements to both nanocrystal fabrication technology and micro-cavity design. Such a gate could serve as an active element in photonic-based quantum technologies.

Photonic quantum technology provides a viable route to quantum communication1,2, quantum simulation3 and quantum information processing4. Recent progress has seen the realization of boson sampling using 20 single photons3 and quantum key distribution over hundreds of kilometres2. Scaling the complexity requires architectures containing multiple photon sources, photon counters and a large number of indistinguishable single photons. Semiconductor quantum dots are bright and fast sources of coherent single photons5-9. For applications, a roadblock is the poor quantum coherence on interfering single photons created by independent quantum dots10,11. Here we demonstrate two-photon interference with near-unity visibility (93.0 ± 0.8)% using photons from two completely separate GaAs quantum dots. The experiment retains all the emission into the zero phonon line-only the weak phonon sideband is rejected; temporal post-selection is not employed. By exploiting quantum interference, we demonstrate a photonic controlled-not circuit and an entanglement with fidelity of (85.0 ± 1.0)% between photons of different origins. The two-photon interference visibility is high enough that the entanglement fidelity is well above the classical threshold. The high mutual coherence of the photons stems from high-quality materials, diode structure and relatively large quantum dot size. Our results establish a platform-GaAs quantum dots-for creating coherent single photons in a scalable way.

High average output power femtosecond sources operating across the 1.5 µm telecommunication band are restricted mainly to colour-centre lasers, Kerr-lens modelocked Cr+4:YAG oscillators and optical parametric oscillators (OPOs). The need for cryogenic conditions limits the versatility of colour-centre-based souces and practical difficulties have made self modelocked operation of Cr−4:YAG lasers near the 1.4 µm water absorption band very difficult to sustain. In contrast, the OPO that we describe in this paper operates at room temperature and is continuouslv-tunable over 200 nm from 1.375 to 1.575 µm using only a single cavity mirror set. The OPO is based on periodically poled RbTiOAsO4 (PPRTA)1. The crystal used had a grating period of 30 µm and dimensions 5 mm long × 0.5 mm width × 5 mm high2. The crystal was antireflection coated for a wavelength of 1.1 µm and we estimate that the loss of each surface at a wavelength of 1.5 µm to be ~1 %. The OPO was synchronously pumped by a modelocked Ti:sapphire laser at a repetition rate of 84 MHz. with output pulses of 100 fs duration and centred at a wavelength of 850 nm. We used a 90 mm focal-length lens to focus the pump beam in to the PPRTA crystal. The polarisation of the pump, signal and idler wavelengths were all horizontal in the cavity and parallel to the poling direction which lay along the crystalographic c axis. The dispersion-compensated OPO cavity consisted of two SF14 prisms, two curved mirrors (r = 100 mm) and one flat mirror as the output coupler. All the mirrors were high-reflecting at the central wavelength of 1.5 µm.

The evolution characteristics of the degenerate four-wave mixing (DFWM) effect in the proposed tellurite photonic crystal fiber (PCF) are investigated systematically. The influence of the pitch distance and diameter-to-pitch ratio on the phase-matching condition is analyzed numerically. The effects of fiber length, signal wavelength, idler wavelength, initial pump power and initial signal power on the signal gain and idler conversion efficiency are investigated. Based on the DFWM occurring in the proposed tellurite PCF, the signal (anti-Stokes) wave is efficiently amplified and the idler (Stokes) wave is efficiently generated at the mid-infrared (mid-IR) waveband with the pump wavelength of 1.553 μm. The signal gain can be increased by increasing the initial pump power. The idler conversion efficiency can reach ~ 26%. The simulated results will be instructive for the experimental FWM process to generate mid-IR optical parametric oscillators.

Quantum-photonic chips, which integrate quantum light sources alongside active and passive optical elements, as well as single-photon detectors, show great potential for photonic quantum information processing and quantum technology. Mature semiconductor nanofabrication processes allow for scaling such photonic integrated circuits to on-chip networks of increasing complexity. Second-order nonlinear materials are the method of choice for generating photonic quantum states in the overwhelming majority of linear optic experiments using bulk components, but integration with waveguide circuitry on a nanophotonic chip proved to be challenging. Here, we demonstrate such an on-chip parametric down-conversion source of photon pairs based on second-order nonlinearity in an aluminum-nitride microring resonator. We show the potential of our source for quantum information processing by measuring the high visibility anti-bunching of heralded single photons with nearly ideal state purity. Our down-conversion source yields measured coincidence rates of 80 Hz, which implies MHz generation rates of correlated photon pairs. Low noise performance is demonstrated by measuring high coincidence-to-accidental ratios. The generated photon pairs are spectrally far separated from the pump field, providing great potential for realizing sufficient on-chip filtering and monolithic integration of quantum light sources, waveguide circuits and single-photon detectors.

We experimentally demonstrate tunable dual channel broadcasting of a signal over the C-band for wavelength division multiplexed (WDM) optical networks. This is based on cascaded χ(2) nonlinear mixing processes in a specially engineered, 20-mm-long step-chirped periodically poled lithium niobate with a broad 28-nm second harmonic (SH) bandwidth in the 1.55-μm spectral range. A 10-GHz picosecond mode-locked laser was used as a signal along with a CW pump to generate two pulsed idlers, which are simultaneously tuned across the C-band by detuning of the pump wavelength within the broad SH bandwidth. Variable-input, variable-output scheme of tuned idlers is successfully achieved by tuning the signal wavelength. Pump or signal wavelength tuning of ~10 nm results in the idlers spreading across 30 nm in the C-band.

The output characteristics of light in two parametric generation regimes [parametric superluminescence and parametric generation in a singly resonant optical parametric oscillator (OPO) based on a 50-mm long PPLN crystal, synchronously pumped by a 50-ps Nd : YAG laser] are compared. The total average output power at the wavelengths of signal (λ = 1475 nm) and idler (λ = 3820 nm) waves in the superluminescence regime is ∼120 mW (peak power ∼120 kW). The maximum total conversion efficiency with respect to the absorbed power in the superluminescence regime is ∼60%. The maximum conversion efficiency into the idler wave with respect to the absorbed pump power is 15% and 25% (quantum efficiencies of 54% and 90%) for the superluminescence and singly resonant OPO regimes, respectively. The maximum values of the average output power at the idler wavelength are ∼30 and ∼60 mW at degrees of pump depletion of 47% and 55% for the superluminescence and singly resonant OPO regimes, respectively.

A multiwavelength midinfrared quasi-phase-matched (QPM) difference frequency generation (DFG) scheme is proposed based on a segmented temperature controlling technique for the uniform grating periodically poled lithium niobate (PPLN). The QPM DFG output performances have been investigated under the fixed pump and signal wavelength conditions, respectively. Our theoretical results show that when the pump wavelength is fixed at 1.08 μm, three idler QPM bands, located at 3.46, 3.50, and 3.57 μm, have been obtained, where the temperatures of the three PPLN segments with the same length are set at 20°C, 70°C, and 100°C. However, when the signal wavelength is fixed at 1.58 μm, six idler QPM bands, located at 2.95, 3.06, 3.14, 3.63, 3.72, and 3.83 μm, have been achieved with the same crystal temperature distribution of 20°C, 70°C, and 100°C.