Versatile photonic molecule switch in multimode microresonators

Physical systems with discrete energy levels are ubiquitous in nature and are fundamental building blocks of quantum technology. Realizing controllable artifcial atom- and molecule-like systems for light would allow for coherent and dynamic control of the frequency, amplitude and phase of photons. In this work, we demonstrate a photonic molecule with two distinct energy-levels and control it by external microwave excitation. We show signature two-level dynamics including microwave induced photonic Autler-Townes splitting, Stark shift, Rabi oscillation and Ramsey interference. Leveraging the coherent control of optical energy, we show on-demand photon storage and retrieval in optical microresonators by reconfguring the photonic molecule into a bright-dark mode pair. These results of dynamic control of light in a programmable and scalable electro-optic platform open doors to applications in microwave photonic signal processing, quantum photonics in the frequency domain, optical computing concepts and simulations of complex physical systems.

High nonlinearity, low or negligible two-photon absorption, and CMOS-compatibility make hydrogenated amorphous silicon an attractive platform for integrated nonlinear optical signal processing devices. Recent nonlinear optical demonstrations are discussed as well as material property investigations.

Polycrystalline SrBi4Ti4O15 thin films with good morphology and layered perovskite structure were fabricated on fused silica substrates using r f magnetron sputtering system at various oxygen mixing percentages (25 and 50). The crystallite sizes of the particles are in 17-28 nm range. The Nonlinear optical properties were investigated by using Z-scan method at a wavelength of 800 nm with 2 ps duration pulses. The films exhibit the fast and giant optical nonlinearities having the two-photon absorption coefficient (β) with magnitude of 10−8-10−9 cm/W and the nonlinear refraction coefficient of ∼10−12 cm2/W. These results indicate SrBi4Ti4O15 thin films are promising candidates for applications in nonlinear optical and optical signal processing devices.

Femtosecond time-resolved dynamics of exciton screening and pairing is studied in a 53-\AA{} GaAs multiple-quantum-well structure at 15 and 224 K. An intriguing high-energy shift of the exciton self-energy in the dense limit is reported.

Nonlinear optical signal processing by ultrafast Raman pulses in silicon-on-insulator rib waveguides is theoretically investigated in this paper. Stimulated Raman scattering, two-photon absorption, free carrier dispersion, self- and cross-phase-modulation-induced by Kerr effect, walk-off, group velocity dispersion, pump depletion, self-steeping, and polarization coupling are taken into account by a very general modeling under subpicosecond regime. Raman amplification, multiwavelength conversion, soliton formation, and pulse compression are presented and discussed. Finally, some simulations for generation of higher order Stokes pulses in mid-IR region are given.

Photonic integration is an enabling technology for photonic quantum science, offering greater scalability, stability, and functionality than traditional bulk optics. Here, we describe a scalable, heterogeneous III-V/silicon integration platform to produce Si3N4 photonic circuits incorporating GaAs-based nanophotonic devices containing self-assembled InAs/GaAs quantum dots. We demonstrate pure single-photon emission from individual quantum dots in GaAs waveguides and cavities - where strong control of spontaneous emission rate is observed - directly launched into Si3N4 waveguides with > 90 % efficiency through evanescent coupling. To date, InAs/GaAs quantum dots constitute the most promising solid state triggered single-photon sources, offering bright, pure and indistinguishable emission that can be electrically and optically controlled. Si3N4 waveguides offer low-loss propagation, tailorable dispersion and high Kerr nonlinearities, desirable for linear and nonlinear optical signal processing down to the quantum level. We combine these two in an integration platform that will enable a new class of scalable, efficient and versatile integrated quantum photonic devices.

We describe recent work on using time-lens techniques to magnify, compress, and cloak optical signals with bandwidths exceeding a terahertz. Article not available.

Employment of optical techniques in signal processing and communication and computing systems has become a major research and development effort at many industrial, government, and university laboratories across the nation and in Europe and Japan. implementation of optical computing concepts and the use of bistable etalons and non-linear logic devices in computing have gained a lot of support and enthusiasm from the optics community in recent years. The significance Iof this field and its potential importance in future technologies is evidenced by the large number of conferences, workshops, and special issues on the subject.

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To achieve high reliability in nonlinear optical signal processing in optical networks, we propose an all-optical limiter with high-accuracy thresholding based on self-phase modulation (SPM) assisted by preparatory waveform conversion. By converting an input pulse into a super-Gaussian one to be fed into an optical fibre for SPM, we can achieve the function of an optical limiter with high-accuracy thresholding which enables a precise stabilization of the intensities of optical signals. The simulation results show that the proposed optical limiter realizes a very accurate thresholding by which the intensity fluctuation is stabilized to less than 0.06 dB, for a relatively wide input range of 5.4 dB.

Four-wave mixing, a pivotal nonlinear process in optical signal processing, is significantly enhanced in microring resonators due to their inherent high power enhancement. However, these resonators traditionally face challenges in the precise modulation of coupling strength and phase shift within photonic integrated circuits. In this study, we present fully tunable coupled resonators, termed a photonic molecule device, drawing a parallel between the interactions of its optical cavities and those found within molecules. It incorporates an electrostatic micro-electromechanical system (MEMS), allowing for precise control. Unlike previous photonic molecule devices that could not adjust the coupling strength, this is the first device for four-wave mixing that enables tuning of both the coupling ratio and phase. This enables fine-tuning of the coupling strength and resonant frequencies for each microring, providing the advantage of wavelength controllability in the four-wave mixing process, as well as new parameters for optimizing the conversion efficiency. This innovation in tunability markedly broadens the functionality and application range of the four-wave mixing process.

Polarization of photons plays a key role in quantum optics and light-matter interactions, however, it is difficult to control in nanosystems since the eigenstate of a nanophotonic cavity is usually fixed and linearly polarized. Here, we reveal the polarization control of photons using photonic molecules (PMs) that host supermodes of two coupled nanobeam cavities. In contrast to conventional PMs in a 2D photonic crystal slab, for the two 1D photonic crystal nanobeam cavities the shift and gap between them can be tuned continuously. With an ultra subwavelength gap, the coupling between the two cavities is dominated by the evanescent wave coupling in the surrounding environment, rather not the emission wave coupling for conventional PMs. As such, the non-Hermiticity of the system becomes pronounced, and the supermodes consist of a non-trivial phase difference between bare eigenstates that supports elliptical polarization. We observe that both the polarization degree and polarization angle of the antisymmetric mode strongly depend on the shift and gap between the two cavities, exhibiting polarization states from linear to circular. This full polarization control indicates the great potential of PMs in quantum optical devices and spin-resolved cavity quantum electrodynamics.

The 19 invited and 30 contributed papers in this special issue focus on nonlinear-optical signal processing.

Cavity modes modulation using photonic molecules

This work takes inspiration from chemistry where the spectral characteristics of the molecules are determined by hybridization of electronic states evolving from the individual atomic orbitals. Based on analogy between quantum mechanics and the classical electrodynamics, we sorted dielectric microspheres with almost identical positions of their whispering gallery mode (WGM) resonances. Using these microspheres as classical photonic atoms, we assembled them in a wide range of structures including linear chains and planar photonic molecules. We studied WGM hybridization effects in such structures using side coupling by tapered microfibers as well as finite difference time domain modeling. We demonstrated that the patterns of WGM spectral splitting are representative of the symmetry, number of constituting atoms and topology of the photonic molecules which in principle can be viewed as “spectral signatures” of various molecules. We also show new ways of controlling WGM coupling constants in such molecules. Excellent agreement was found between measured transmission spectra and spectral signatures of photonic molecules predicted by simulation. image