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The study has demonstrated a novel microcavity‐based flexible photon up‐conversion system using second harmonic generation (SHG) from a polar nematic fluidic medium doped with a laser dye. The idea is based on coherent light generation via stimulated emission (lasing) and simultaneous frequency doubling inside a microcavity. The polar nematic fluid equips very high even‐order optical nonlinearity due to its polar symmetry and large dipole moment along the molecular long axis. At the same time, its inherent fluidic nature allows to easily functionalize the media just by doping, in the present case, with an emissive laser dye. The demonstrated system exhibits a giant nonlinear optical response to input light, while enabling spectral narrowing and multiple‐signal output of up‐converted light, which is not attainable through the simple SH‐conversion of input light. Furthermore, the susceptibility of the liquid crystal offers dynamic modulation capabilities by an external stimulus, such as signal switching by the application of electric field or wavelength tuning through temperature variation. Such a brand‐new type of simple coherent flexible up‐conversion system must be promising as a new principle for easily accessible and down‐scalable wavelength conversion devices. [ABSTRACT FROM AUTHOR]

2D moiré superlattices offer a versatile platform for manipulating quantum materials, exploiting their spatially varying atomic registry to modify electronic structures, resulting in the emergence of flat electronic minibands, enhanced electronic interactions, and the onset of novel quantum phenomena. Despite extensive investigations into moiré excitons within twisted bilayer moiré superlattices, the interplay between moiré superlattices and optical microcavities remains elusive. Here, a WSe2 homobilayer with a small twist angle positioned on optical microcavities atop a SiO2 (285 nm)/Si substrate is investigated. Utilizing low‐temperature photoluminescence (PL) spectroscopy, it is observed that the twisted homobilayer at the edge of the optical cavity (Edge‐THB) exhibits enhanced localization of moiré excitons and a deeper moiré potential. This behavior is attributed to the combined influence of strain induced by the optical microcavity structure on the moiré superlattice and the amplification of the electromagnetic field. Furthermore, the existence of moiré excitons through a comprehensive analysis, encompassing temperature‐dependent PL spectra, circularly polarized PL spectra, and Landé g‐factor measurements for Edge‐THB is validated. These findings provide valuable insights into the intricate interaction between moiré superlattices and optical microcavities, paving the way for future applications in quantum technologies. [ABSTRACT FROM AUTHOR]

In recent years, high quality factor echo wall mode optical microcavities have developed rapidly and become a hot research topic in the fields of optics and physics. Optical microcavity is a kind of micro optical element. Due to its small size and high-quality factor, it can enhance the interaction between light and matter, enabling long-time light stays. Echo wall mode resonators are one of the typical representatives of optical microcavities, with advantages of small size, high sensitivity, and long life. Currently, applications based on echo wall mode resonators are mainly concentrated in various fields such as sensors, lasers, filters, and so on. However, current research on echo wall mode resonators has not yet achieved large-scale production, and is only in the laboratory research stage. Industrial production still has shortcomings such as high cost and manufacturing process difficulties. This article focuses on the research progress of echo wall mode resonators, expounds the impact of echo wall materials on Q values, and discusses the applications of echo wall mode resonators in the fields of sensors, lasers, and filters in recent years. It also proposes the challenges and further research directions of echo wall mode resonators in the future, which may realize all-optical networks. For further research directions, we believe that it is necessary to reduce costs, shorten time, and improve the accuracy and efficiency of the preparation process. It is also necessary to solve the coupling problem between the microcavity and the optical device, improving the coupling efficiency and the anti-interference ability. It should also address the sensitivity of the cavity to the environment to ensure that the microcavity has good stability when preparing devices such as filters.

The field of compact optical microcavities has received significant research in the past decades, and a broad range of cavity‐based micromechanical sensors has been demonstrated. The present approach replaces the frequently employed, complex etched cantilever and membrane structures with a simple thin‐film system based on a compressible photonic microcavity to achieve pressure‐sensitive wavelength shifting of resonant modes. The effects of a topological dielectric mirror architecture on the light propagation in the system are extensively investigated. Topologically improved light‐matter interaction is experimentally demonstrated for systems where thin‐film devices are mounted on one side of the photonic cavity due to mechanical constraints. Coupled topological states are examined under the aspect of mode splitting and exhibit advantageous splitting tunability compared to non‐topological systems. The findings are complemented by the proposal of a simple spectral evaluation method allowing significant improvement in the precision of integrated Fabry‐Pérot sensors. The readout concept of the presented sensor allows a scalable improvement of the measurement precision by evaluating the resonant‐mode order in the deformable cavity. The experimental results and conceptual advancements provide pathways for significant improvements addressing the efficiency of light‐matter interaction in Fabry‐Pérot cavities and the readout precision of sensors incorporating thin‐film photodiodes in multimode photonic cavities. [ABSTRACT FROM AUTHOR]

We report a thin-film optical amplifier integrated on a fiber facet based on polymer-coated distributed feedback (DFB) microcavities, which are fabricated on a planar substrate and then transferred onto fiber tips by means of a flexible transfer technique. The amplified light directly couples into the fiber and is detected when coupled out at the other end after propagating along the fiber for about 20 cm. A prominently amplification factor of about 4.33 at 578.57 nm is achieved by sending supercontinuum pulses into the hundreds of micrometers' DFB microcavities along the normal direction, which is also the axis direction of the fiber. The random distortions of grating lines generated during the transfer process result in a larger amplification spectral range and a less strict polarization dependence for injected light. Benefitting from the device size of hundreds of micrometers and the ease of integration, polymer amplifiers based on DFB microcavities demonstrate significant application potentials in optical communication systems and miniaturized optical devices. [ABSTRACT FROM AUTHOR]

Effective schemes are proposed for the generation of bipartite Bell states and theoretically scaling up to arbitrary multiparticle Greenberger–Horne–Zeilinger, cluster, and W states among quantum-dot (QD) spins. They are realized based on the interaction between an single incident photon and single QD spin. Errors from system nonuniformity and defective photon scattering are transformed into detectable photon losses. In the event of a failed experiment, the system allows for the reinjection of a single photon and the reinitiation of the quantum circuit, until a successful outcome is achieved. This loss-prediction and experiment-repeatability approach ensures that the schemes are implemented with uniform and robust fidelity. Compared with the previous methods, these schemes significantly simplify experimental procedures and analysis processes. Furthermore, upon successful execution of the experiment, the use of single-photon detector can faithfully differentiate between various types of entangled states, depending on the initial states of the QD spins. An analysis of the feasibility of the schemes under current experimental parameters suggests high efficiency even in the weak coupling region. [ABSTRACT FROM AUTHOR]

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Abstract The study has demonstrated a novel microcavity‐based flexible photon up‐conversion system using second harmonic generation (SHG) from a polar nematic fluidic medium doped with a laser dye. The idea is based on coherent light generation via stimulated emission (lasing) and simultaneous frequency doubling inside a microcavity. The polar nematic fluid equips very high even‐order optical nonlinearity due to its polar symmetry and large dipole moment along the molecular long axis. At the same time, its inherent fluidic nature allows to easily functionalize the media just by doping, in the present case, with an emissive laser dye. The demonstrated system exhibits a giant nonlinear optical response to input light, while enabling spectral narrowing and multiple‐signal output of up‐converted light, which is not attainable through the simple SH‐conversion of input light. Furthermore, the susceptibility of the liquid crystal offers dynamic modulation capabilities by an external stimulus, such as signal switching by the application of electric field or wavelength tuning through temperature variation. Such a brand‐new type of simple coherent flexible up‐conversion system must be promising as a new principle for easily accessible and down‐scalable wavelength conversion devices.

The combination of higher-order topological insulators and valley photonic crystals has recently aroused extensive attentions due to the great potential in flexible and efficient optical field manipulations. Here, we computationally propose a photonic device for the 1550 nm communication band, in which the topologically protected electromagnetic modes with high quality can be selectively triggered and modulated on demand. Through introducing two valley photonic crystal units without any structural alteration, we successfully achieve multi-dimensional coupled topological states thanks to the diverse electromagnetic characteristics of two valley edge states. According to the simulations, the constructed topological photonic devices can realize Fano lines on the spectrum and show high-quality localized modes by tuning the coupling strength between the zero-dimensional valley corner states and the one-dimensional valley edge states. Furthermore, we extend the valley-locked properties of edge states to higher-order valley topological insulators, where the selected corner states can be directionally excited by chiral source. More interestingly, we find that the modulation of multi-dimensional coupled photonic topological states with pseudospin dependence become more efficient compared with those uncoupled modes. This work presents a valuable approach for multi-dimensional optical field manipulation, which may support potential applications in on-chip integrated nanophotonic devices. [ABSTRACT FROM AUTHOR]

Raman microlasers form on-chip versatile light sources by optical pumping, enabling numerical applications ranging from telecommunications to biological detection. Stimulated Raman scattering (SRS) lasing has been demonstrated in optical microresonators, leveraging high Q factors and small mode volume to generate downconverted photons based on the interaction of light with the Stokes vibrational mode. Unlike redshifted SRS, stimulated anti-Stokes Raman scattering (SARS) further involves the interplay between the pump photon and the SRS photon to generate an upconverted photon, depending on a highly efficient SRS signal as an essential prerequisite. Therefore, achieving SARS in microresonators is challenging due to the low lasing efficiencies of integrated Raman lasers caused by intrinsically low Raman gain. In this work, high-Q whispering gallery microresonators were fabricated by femtosecond laser photolithography assisted chemo-mechanical etching on thin-film lithium niobate (TFLN), which is a strong Raman-gain photonic platform. The high Q factor reached 4.42 × 106, which dramatically increased the circulating light intensity within a small volume. And a strong Stokes vibrational frequency of 264 cm−1 of lithium niobate was selectively excited, leading to a highly efficient SRS lasing signal with a conversion efficiency of 40.6%. And the threshold for SRS was only 0.33 mW, which is about half the best record previously reported on a TFLN platform. The combination of high Q factors, a small cavity size of 120 μm, and the excitation of a strong Raman mode allowed the formation of SARS lasing with only a 0.46 mW pump threshold. [ABSTRACT FROM AUTHOR]

Abstract Optical microcavities have the ability to confine photons in small mode volumes for long periods of time, greatly enhancing light-matter interactions, and have become one of the research hotspots in international academia. In recent years, sensing applications in complex environments have inspired the development of multimode optical microcavity sensors. These multimode sensors can be used not only for multi-parameter detection but also to improve measurement precision. In this review, we introduce multimode sensing methods based on optical microcavities and present an overview of the multimode single/multi-parameter optical microcavities sensors. Expected further research activities are also put forward. Graphical abstract

We report a thin-film optical amplifier integrated on a fiber facet based on polymer-coated distributed feedback (DFB) microcavities, which are fabricated on a planar substrate and then transferred onto fiber tips by means of a flexible transfer technique. The amplified light directly couples into the fiber and is detected when coupled out at the other end after propagating along the fiber for about 20 cm. A prominently amplification factor of about 4.33 at 578.57 nm is achieved by sending supercontinuum pulses into the hundreds of micrometers’ DFB microcavities along the normal direction, which is also the axis direction of the fiber. The random distortions of grating lines generated during the transfer process result in a larger amplification spectral range and a less strict polarization dependence for injected light. Benefitting from the device size of hundreds of micrometers and the ease of integration, polymer amplifiers based on DFB microcavities demonstrate significant application potentials in optical communication systems and miniaturized optical devices.

The combination of higher-order topological insulators and valley photonic crystals has recently aroused extensive attentions due to the great potential in flexible and efficient optical field manipulations. Here, we computationally propose a photonic device for the 1550 nm communication band, in which the topologically protected electromagnetic modes with high quality can be selectively triggered and modulated on demand. Through introducing two valley photonic crystal units without any structural alteration, we successfully achieve multi-dimensional coupled topological states thanks to the diverse electromagnetic characteristics of two valley edge states. According to the simulations, the constructed topological photonic devices can realize Fano lines on the spectrum and show high-quality localized modes by tuning the coupling strength between the zero-dimensional valley corner states and the one-dimensional valley edge states. Furthermore, we extend the valley-locked properties of edge states to higher-order valley topological insulators, where the selected corner states can be directionally excited by chiral source. More interestingly, we find that the modulation of multi-dimensional coupled photonic topological states with pseudospin dependence become more efficient compared with those uncoupled modes. This work presents a valuable approach for multi-dimensional optical field manipulation, which may support potential applications in on-chip integrated nanophotonic devices.

Most of the previous TMDC-photon coupling devices were mainly based on A exciton due to its high oscillator strength and large exciton binding energy. Less effort has been focused on the modulation of the emission of B exciton and Rydberg states in TMDCs, especially in monolayer WS2. Here, we demonstrate that the photoluminescence (PL) emission of WS2-microcavity coupling devices can be tailored in a broad visible wavelength range (490 nm–720 nm). In contrast to the intrinsic PL emission of monolayer WS2, 25-fold enhanced B exciton emission and significant PL emission from the 2s Rydberg state can be observed. From the transient absorption (TA) measurements, the strongly coupled hybrid states based on B exciton can be remarkably fingerprinted. Furthermore, the strongly enhanced PL emission from the coupled B exciton has been demonstrated due to the strongly increased lower polariton (LP) state population and the internal conversion pathway being blocked in the strong coupling regime. Besides, the remarkable PL emission from the 2s Rydberg state is also revealed and confirmed by the additional ground state bleaching signal in TA spectra. These physical mechanisms about tailoring the PL emission in low dimensional TMDCs can provide significant references for constructing highly efficient optoelectronic devices.

Abstract Optical microcavities have emerged as promising platforms for ultrasound detection. One of the main tendencies in recent studies is to develop high-Q microresonators for ultrasensitive ultrasound detection, while the nonlinear optical effects become significant but are generally neglected. Here, we propose a thermal-assisted microcavity Raman laser for ultrasound detection. Acoustic waves modulate the resonant frequency of the cavity mode, altering the coupled efficiency of a fixed-wavelength input laser, and therefore the output Raman power. Experimentally, the noise equivalent pressure reaches as low as 8.1 Pa at 120 kHz in air. Besides, it is found that the thermal effect involved in high-Q microcavities can compensate for the low-frequency noises, while without degrading their sensitivity to high-frequency acoustic waves above hundreds of kilohertz. Therefore, it enables long-standing stability during the measurements due to the natural resistance to laser frequency drifts and environmental disturbances, which holds great potential in practical applications of ultrasound sensing and imaging.

An accurate knowledge of the optical properties of β-Ga2O3 is key to developing the full potential of this oxide for photonics applications. In particular, the dependence of these properties on temperature is still being studied. Optical micro- and nanocavities are promising for a wide range of applications. They can be created within microwires and nanowires via distributed Bragg reflectors (DBR), i.e., periodic patterns of the refractive index in dielectric materials, acting as tunable mirrors. In this work, the effect of temperature on the anisotropic refractive index of β-Ga2O3 n(λ,T) was analyzed with ellipsometry in a bulk crystal, and temperature-dependent dispersion relations were obtained, with them being fitted to Sellmeier formalism in the visible range. Micro-photoluminescence (μ-PL) spectroscopy of microcavities that developed within Cr-doped β-Ga2O3 nanowires shows the characteristic thermal shift of red–infrared Fabry–Perot optical resonances when excited with different laser powers. The origin of this shift is mainly related to the variation in the temperature of the refractive index. A comparison of these two experimental results was performed by finite-difference time-domain (FDTD) simulations, considering the exact morphology of the wires and the temperature-dependent, anisotropic refractive index. The shifts caused by temperature variations observed by μ-PL are similar, though slightly larger than those obtained with FDTD when implementing the n(λ,T) obtained with ellipsometry. The thermo-optic coefficient was calculated. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMD) heterostructure is widely applied for second harmonic generation (SHG) and holds great promises for laser source, nonlinear switch, and optical logic gate. However, for atomically thin TMD heterostructures, low SHG conversion efficiency would occur due to reduction of light—matter interaction length and lack of phase matching. Herein, we demonstrated a facile directional SHG amplifier formed by MoS2/WS2 monolayer heterostructures suspended on a holey SiO2/Si substrate. The SHG enhancement factor reaches more than two orders of magnitude in a wide spectral range from 355 to 470 nm, and the radiation angle is reduced from 38° to 19° indicating higher coherence and better emission directionality. The giant SHG enhancement and directional emission are attributed to the great excitation and emission field concentration induced by a self-formed vertical Fabry—Pérot microcavity. Our discovery gives helpful insights for the development of two-dimensional (2D) nonlinear optical devices. [ABSTRACT FROM AUTHOR]

Raman microlasers form on-chip versatile light sources by optical pumping, enabling numerical applications ranging from telecommunications to biological detection. Stimulated Raman scattering (SRS) lasing has been demonstrated in optical microresonators, leveraging high Q factors and small mode volume to generate downconverted photons based on the interaction of light with the Stokes vibrational mode. Unlike redshifted SRS, stimulated anti-Stokes Raman scattering (SARS) further involves the interplay between the pump photon and the SRS photon to generate an upconverted photon, depending on a highly efficient SRS signal as an essential prerequisite. Therefore, achieving SARS in microresonators is challenging due to the low lasing efficiencies of integrated Raman lasers caused by intrinsically low Raman gain. In this work, high-Q whispering gallery microresonators were fabricated by femtosecond laser photolithography assisted chemo-mechanical etching on thin-film lithium niobate (TFLN), which is a strong Raman-gain photonic platform. The high Q factor reached 4.42 × 106, which dramatically increased the circulating light intensity within a small volume. And a strong Stokes vibrational frequency of 264 cm−1 of lithium niobate was selectively excited, leading to a highly efficient SRS lasing signal with a conversion efficiency of 40.6%. And the threshold for SRS was only 0.33 mW, which is about half the best record previously reported on a TFLN platform. The combination of high Q factors, a small cavity size of 120 μm, and the excitation of a strong Raman mode allowed the formation of SARS lasing with only a 0.46 mW pump threshold.

Benefited from abundant long-lived intermediate energy levels of rear earth elements, large anti-Stokes lasing can be realized by multi-photon upconversion processes, which does not demand rigorous phase match and ultrahigh pump power. Here, we have fabricated an Er-doped silica microsphere with an ultrahigh intrinsic quality factor of 1.2 × 108. By continuous-wave (CW) excitation at 1535 nm, four- and five-photon upconversion lasers are achieved simultaneously under room temperature, in which the lasing thresholds are estimated as 176 and 600 μW, respectively. Beside the ultralow thresholds, the microlaser also exhibits good stability of lasing intensity for practical applications. The four- and five-photon upconversion lasing from rare earth elements have not been separately demonstrated under CW pump and room temperature until this work. This demonstration provides a prospect to realizing high-performance short-wavelength laser by pumping low-energy photons.

Organic circularly polarized (CP) lasers have received increasing attention due to their future photoelectric applications. Here, we demonstrate a CP laser from a pure organic crystal‐filled microcavity without any chiral molecules or chiral structures. Benefited from the giant anisotropy and excellent laser gain of organic crystals, optical Rashba‐Dresselhaus spin‐orbit coupling effect can be induced and is conductive to the CP laser in such microcavities. The maximum dissymmetry factor of the CP lasing with opposite helicities reachs 1.2. Our strategy may provide a new idea for the design of CP lasers towards future 3D laser displays, information storage and other fields. [ABSTRACT FROM AUTHOR]

Most of the previous TMDC-photon coupling devices were mainly based on A exciton due to its high oscillator strength and large exciton binding energy. Less effort has been focused on the modulation of the emission of B exciton and Rydberg states in TMDCs, especially in monolayer WS2. Here, we demonstrate that the photoluminescence (PL) emission of WS2-microcavity coupling devices can be tailored in a broad visible wavelength range (490 nm–720 nm). In contrast to the intrinsic PL emission of monolayer WS2, 25-fold enhanced B exciton emission and significant PL emission from the 2s Rydberg state can be observed. From the transient absorption (TA) measurements, the strongly coupled hybrid states based on B exciton can be remarkably fingerprinted. Furthermore, the strongly enhanced PL emission from the coupled B exciton has been demonstrated due to the strongly increased lower polariton (LP) state population and the internal conversion pathway being blocked in the strong coupling regime. Besides, the remarkable PL emission from the 2s Rydberg state is also revealed and confirmed by the additional ground state bleaching signal in TA spectra. These physical mechanisms about tailoring the PL emission in low dimensional TMDCs can provide significant references for constructing highly efficient optoelectronic devices. [ABSTRACT FROM AUTHOR]

Photosynthesis is one the most important biological processes on earth, producing life-giving oxygen, and is the basis for a large variety of plant products. Measurable properties of photosynthesis provide information about its biophysical state, and in turn, the physiological conditions of a photoautotrophic organism. For instance, the chlorophyll fluorescence intensity of an intact photosystem is not constant as in the case of a single fluorescent dye in solution but shows temporal changes related to the quantum yield of the photosystem. Commercial photosystem analyzers already use the fluorescence kinetics characteristics of photosystems to infer the viability of organisms under investigation. Here, we provide a novel approach based on an optical Fabry–Pérot microcavity that enables the readout of photosynthetic properties and activity for an individual cyanobacterium. This approach offers a completely new dimension of information, which would normally be lost due to averaging in ensemble measurements obtained from a large population of bacteria. [ABSTRACT FROM AUTHOR]

Optical microcavities have emerged as promising platforms for ultrasound detection. One of the main tendencies in recent studies is to develop high-Q microresonators for ultrasensitive ultrasound detection, while the nonlinear optical effects become significant but are generally neglected. Here, we propose a thermal-assisted microcavity Raman laser for ultrasound detection. Acoustic waves modulate the resonant frequency of the cavity mode, altering the coupled efficiency of a fixed-wavelength input laser, and therefore the output Raman power. Experimentally, the noise equivalent pressure reaches as low as 8.1 Pa at 120 kHz in air. Besides, it is found that the thermal effect involved in high-Q microcavities can compensate for the low-frequency noises, while without degrading their sensitivity to high-frequency acoustic waves above hundreds of kilohertz. Therefore, it enables long-standing stability during the measurements due to the natural resistance to laser frequency drifts and environmental disturbances, which holds great potential in practical applications of ultrasound sensing and imaging. [ABSTRACT FROM AUTHOR]

In this work, a hollow cylindrical optical microcavity is numerically investigated by finite-difference time-domain simulations. Enhancement of a single whispering-gallery mode (WGM) is realized by inserting a periodic hole array into the hollow cylindrical structure. Line of missing holes acts as an optical microcavity. Electric and magnetic field profiles of both typical and enhanced resonant modes are presented. Variations of the single-mode resonant frequency and its quality (Q) factor are studied as a function of structural parameters, which are hole radius, width of the missing hole line, and number of holes. This work shows that the hole radius and the width of the missing hole line strongly affect both the resonant frequency and Q factor while varying the number of holes does not influence the resonant frequency, but they monotonically change the Q factor. This work provides information for designing and optimizing an WGM optical microcavity.

Surface-enhanced Raman spectroscopy (SERS) has been widely investigated and employed as a powerful optical analytical technique providing fingerprint vibrational information of molecules with high sensitivity and resolution. In addition to metallic nanostructure, dielectric micro-/nano-structures with extraordinary optical manipulation properties have demonstrated capability in enhanced Raman scattering with ultralow energy losses. Here we report a facile cascaded structure composed of a large microsphere (LMS) and a small microsphere array with Ag nanoparticles as a novel hybrid SERS substrate, for the first time. The cascaded microsphere-coupled SERS substrate provides a platform to increase the molecular concentration, boost the intensity of localized excitation light, and direct the far-field emission, for giant Raman enhancement. It demonstrates the maximum enhancement factor of Raman intensity greater than 108 for the limit of detection down to 10−11 M of 4-nitrothiphenol molecules in aqueous solution. The present work inspires a novel strategy to fabricate cascaded dielectric/metallic micro-/nano-structures superior to traditional SERS substrates towards practical applications in cost-effective and ultrahigh-sensitive trace-detection.

The investigation of optical microcavity solitons is in demand both for applications and basic science. Despite the tremendous progress in the study of microresonator solitons, there is still no complete understanding of all features of their nonlinear dynamics in various regimes. Controlling soliton properties is also of great interest. We proposed and investigated experimentally and theoretically a simple and easily reproducible way to generate Raman solitons with controllable spectral width in an anomalous dispersion region in a functionalized silica microsphere with whispering gallery modes (WGMs) driven in a normal dispersion regime. To functionalize the microsphere, coating (TiO2 + graphite powder) was applied at the pole. The coating is used for effective thermalization of the radiation of an auxiliary laser diode launched through the fiber stem holding the microsphere to control detuning of the pump frequency from exact resonance due to the thermo-optical shift of the WGM frequencies. We demonstrated that the thermo-optical control by changing the power of an auxiliary diode makes it possible to switch on/off the generation of Raman solitons and control their spectral width, as well as to switch Raman generation to multimode or single-mode. We also performed a detailed theoretical analysis based on the Raman-modified Lugiato–Lefever equation and explained peculiarities of intracavity nonlinear dynamics of Raman solitons. All experimental and numerically simulated results are in excellent agreement. [ABSTRACT FROM AUTHOR]

A wide-color-gamut display enableby a narrow emission linewidth facilitates a visually immersive experience akin to the real world. Quantum dot light-emitting diodes (QLEDs) with excellent color purity and high efficiency hold great promise as future candidates for high-definition displays. However, most devices typically exhibit emission linewidths exceeding 20 nm, and lack a universal strategy for further enhancing the color purity. In this study, a planar microcavity structure for realizing ultra-narrow emissions is developed by incorporating a distributed Bragg reflector into normal electroluminescent devices. By leveraging the strong optical resonance effect derived from this microcavity structure, red QLEDs are successfully fabricated with an extraordinary full width at half maximum of 11 nm in the normal direction, beyond the BT.2020 color coordinates. The fabricated red-microcavity QLEDs exhibit a considerable enhancement in the external quantum efficiency, which increases from 28.2% to 35.6%, together with an extended operating lifetime. The strategy adopted herein will serve as an effective reference for achieving ultra-narrow emission and high-efficiency QLEDs., (© 2024 Wiley‐VCH GmbH.)

Quantum information networks can transmit quantum states and perform quantum operations between different quantum network nodes, which are essential for various applications of quantum information technology in the future. In this paper, a potentially practical scheme for implementing nonlocal quantum controlled-not (CNOT) gate operations on quantum-dot-confined electron spins between two quantum network nodes is presented. The scheme can realize parallel teleportation of two nonlocal quantum CNOT gates simultaneously by employing hyperentangled photon pairs to establish quantum channel, which can effectively improve the channel capacity and operational speed. The core of the scheme are two kinds of photon-spin hybrid quantum CNOT gate working in a failure-heralded and fidelity-robust fashion. With the heralded mechanism, the nonlocal CNOT gates can be implementated with unity fidelities in principle, even if the particularly ideal conditions commonly used in other schemes are not satisfied strictly. Our analysis and calculations indicate that the scheme can be demonstrated efficiently (with efficiency exceeding 99%) with current or near-future technologies. Moreover, the utilized photon-spin hybrid quantum gates can be regarded as universal modules for many other quantum information processing (QIP) tasks. Therefore, the scheme is potential for constructing elementary quantum networks, and realizing nolocal QIP with high channel capacities, high fidelities, and high efficiencies.

Surface‐enhanced Raman spectroscopy (SERS) is a powerful tool for nondestructive and ultrasensitive optical trace‐detection. However, the sophisticated fabrication processes and performance degradation on flexible substrates block SERS for practical uses. Here, we report a facile flexible microsphere‐coupled SERS (McSERS) substrate composed of a dielectric microsphere cavity array (MCA) and random gold nanoparticles (AuNPs) capping on a polydimethylsiloxane (PDMS) film (MCA/AuNPs/PDMS) for giant Raman enhancement. The random distribution of AuNPs provides a hydrophilic surface against to the coffee‐ring effect for uniform localized surface plasmon resonance (LSPR) response. The MCA capped on the AuNPs boosts the Raman intensity via the multiple optical manipulation processes, in which the photonic nanojet (PNJ) confines the excitation intensity near the AuNPs, whispering‐gallery mode (WGM) facilitates the energy transfer from microsphere cavities to AuNP gaps for LSPR boosting, and directional antenna effect converts near‐field Raman signals into far‐field with a small divergence. Therefore, the Raman scattering is dramatically improved with the enhancement factor (EF) to 107 for the limit of detection (LoD) of 4‐nitrobenzenethiol (4‐NBT) molecules down to 0.1 nM, two orders of magnitude higher via MCA coupling. Moreover, the flexible McSERS substrate exhibits outstanding durability and compatibility as an ultrasensitive Raman test strip, by which the thiram concentration is detectable down to 2.42 ng/cm2 on apple peels. The present work provides a facile strategy to fabricate SERS substrates with high flexibility for optical trace‐detection in real‐world applications. [ABSTRACT FROM AUTHOR]

We report a construction of distributed-feedback (DFB) optical microcavities, which is realized through mechanical contact between a high-quality planar thin film of a polymeric semiconductor and a large-area homogeneous nanograting. Using poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3] thiadiazol-4,8-diyl)] (F8BT) as the active medium for the planar layer, we achieve strong amplified spontaneous emission from such a microcavity with a low threshold. This not only simplifies largely the fabrication techniques for DFB microcavities, but also avoids the unexpected chemical interactions during solution processing between the organic semiconductors and the nanograting materials. Furthermore, high-quality polymer thin films with high surface smoothness and high thickness homogeneity are employed without any modulations for constructing the microcavities. This also suggests new designs of microcavity light-emitting diodes, or even for realizing electrically pumped polymer lasers, simply by metallizing the dielectric nanogratings as the electrodes. [ABSTRACT FROM AUTHOR]

Abstract Fiber optofluidic laser (FOFL) integrates optical fiber microcavity and microfluidic channel and provides many unique advantages for sensing applications. FOFLs not only inherit the advantages of lasers such as high sensitivity, high signal-to-noise ratio, and narrow linewidth, but also hold the unique features of optical fiber, including ease of integration, high repeatability, and low cost. With the development of new fiber structures and fabrication technologies, FOFLs become an important branch of optical fiber sensors, especially for application in biochemical detection. In this paper, the recent progress on FOFL is reviewed. We focuse mainly on the optical fiber resonators, gain medium, and the emerging sensing applications. The prospects for FOFL are also discussed. We believe that the FOFL sensor provides a promising technology for biomedical analysis and environmental monitoring.

An accurate knowledge of the optical properties of β-Ga2O3 is key to developing the full potential of this oxide for photonics applications. In particular, the dependence of these properties on temperature is still being studied. Optical micro- and nanocavities are promising for a wide range of applications. They can be created within microwires and nanowires via distributed Bragg reflectors (DBR), i.e., periodic patterns of the refractive index in dielectric materials, acting as tunable mirrors. In this work, the effect of temperature on the anisotropic refractive index of β-Ga2O3 n(λ,T) was analyzed with ellipsometry in a bulk crystal, and temperature-dependent dispersion relations were obtained, with them being fitted to Sellmeier formalism in the visible range. Micro-photoluminescence (μ-PL) spectroscopy of microcavities that developed within Cr-doped β-Ga2O3 nanowires shows the characteristic thermal shift of red–infrared Fabry–Perot optical resonances when excited with different laser powers. The origin of this shift is mainly related to the variation in the temperature of the refractive index. A comparison of these two experimental results was performed by finite-difference time-domain (FDTD) simulations, considering the exact morphology of the wires and the temperature-dependent, anisotropic refractive index. The shifts caused by temperature variations observed by μ-PL are similar, though slightly larger than those obtained with FDTD when implementing the n(λ,T) obtained with ellipsometry. The thermo-optic coefficient was calculated.

Raman spectroscopy is a powerful technique that enables fingerprinting of materials, molecules, and chemical environments by probing vibrational resonances. In many applications, the desired Raman signals are masked by fluorescence, either from the molecular system being studied, or from adjacent metallic nanostructures. Here, it is shown that wavelength‐modulated Raman spectroscopy provides a powerful way to significantly reduce the strength of the fluorescence background, thereby allowing the desired Raman signals to be clearly recorded. This approach is made use of to explore Raman scattering in the context of vibrational strong coupling, an area that has thus far been problematic to visualise. Specifically, strong coupling between the vibrational modes in a polymer and two types of confined light field, the fundamental mode of a metal‐clad microcavity, and the surface‐plasmon modes of an adjacent thin metal film are looked at. While clear advantages in using the wavelength‐modulated Raman approach are found, these results on strong coupling are inconclusive, and highlight the need for more work in this exciting topic area. [ABSTRACT FROM AUTHOR]

Whispering-gallery mode (WGM) microlasers are potential light sources for photonic integrated circuits and optical information processing. In this paper, an integrated twin circular-side octagon microlaser (TCOM) composed of two identical circular-side octagon microcavities (COMs) is proposed and demonstrated for realizing lasing mode control. In a TCOM, we found a global mode with the mode field of an “8” pattern (labeled “8” mode) in addition to weak coupling modes of traditional four-bounce modes. The “8” mode belongs to the whole coupled cavity and is insensitive to the refractive index offset of coupled COMs, but the weak coupling modes are strongly sensitive to the refractive index offset. Lasing mode transformation from multiple coupled modes to a single “8” mode is demonstrated by adjusting the refractive index offset through injection currents. Weak coupling modes for directly connected TCOMs and lasing mode control make the COM a potential unit for large-scale photonic integration and optical information processing. [ABSTRACT FROM AUTHOR]

The present study demonstrates the tuning of optical characteristics of porous silicon (PSi)-based microcavities by N ion beam interactions. These optical microcavities are prepared by using electrochemical etching of heavily doped p+-type Si. The PSi microcavities were exposed to N ions of 200 keV and 1 MeV at an optimized ion fluence of 1 Ă— 1015 ions cmâˆ'2. A significant red-shifting of 32 ∼ 60 nm in the resonance cavity mode was observed due to ion interaction. The experimental results are in good agreement with the transfer matrix simulations. A substantial modification of the PSi microcavity surface states is visualized through Raman and x-ray photoelectron spectroscopy (XPS) techniques. The Raman spectral results show modifications from crystalline Si to nanostructured Si and subsequently to amorphous Si. The XPS indicates the modification of Siâ€"Si and Siâ€"O bonds and the formation of new Siâ€"N bonds, implying the presence of Si3N4. These experimental observations, along with analytical simulations and transfer-matrix method microcavity modeling, conclusively support the realization of cavity tunability and substantial modification in the optical field intensity and photon confinement within the spacer layer of the microcavity. These results suggest that ion beams are the effective tool to produce wider tunable optical properties in microcavities with highly stable designer optical structures suitable for photonic applications. [ABSTRACT FROM AUTHOR]

Optical microcavity, which can localize light at a certain spot for a short period of time, has a wide range of applications, such as optical signal processing and optical frequency combs. Single crystal CaF 2 has excellent optical properties and many research on the manufacturing process to create a microcavity has been done. However, due to its unstable thermal conditions, stable oscillation of Kerr comb could not be done. Single crystal MgF 2 , which also has excellent optical properties, has stable thermal conditions suitable to create a microcavity. Like CaF 2 , MgF 2 microcavity can only be manufactured by ultra-precision cylindrical turning, yet its appropriate processing conditions is not known. In this study, a method to derive the critical depth of cut theoretically in ductile mode machining was proposed in consideration of specific cutting energy, mechanical properties and slip system of workpiece, and tool geometry. The critical depth of cut calculated by the proposed method roughly agreed with the experimental value on the MgF 2 plane. Unlike CaF 2 , MgF 2 has an optical anisotropy; therefore, in order to create a microcavity where the refractive angle is constant, the resonance part needs to be made on a cylinder with (001) plane as end face. Therefore, a microcavity was fabricated according to the critical depth of cut on a cylinder with (001) as end face derived from the proposed method, and the surface integrity was evaluated from the viewpoint of microcavity performance. • A theoretical method to derive the critical depth of cut of crystalline materials is presented. • Geometrical constant χ and critical load at failure P c is redefined to improve the model of brittle material cutting. • The critical depth of cut for CaF 2 and MgF 2 is obtained from P c of one plane or one orthogonal cutting test. • A MgF 2 microcavity is successfully fabricated under the conditions carried out from the presented method. [ABSTRACT FROM AUTHOR]

In this work, a hollow cylindrical optical microcavity is numerically investigated by finite-difference time-domain simulations. Enhancement of a single whispering-gallery mode (WGM) is realized by inserting a periodic hole array into the hollow cylindrical structure. Line of missing holes acts as an optical microcavity. Electric and magnetic field profiles of both typical and enhanced resonant modes are presented. Variations of the single-mode resonant frequency and its quality (Q) factor are studied as a function of structural parameters, which are hole radius, width of the missing hole line, and number of holes. This work shows that the hole radius and the width of the missing hole line strongly affect both the resonant frequency and Q factor while varying the number of holes does not influence the resonant frequency, but they monotonically change the Q factor. This work provides information for designing and optimizing an WGM optical microcavity. [ABSTRACT FROM AUTHOR]

Detuning regulation based on the scanning pump wavelength plays an important role in the generation of temporal solitons in an optical microcavity. Field evolution inside a CaF2 microcavity during the detuning regulation process is demonstrated. It is found that a stable single soliton can be excited when modulation instability dominates in the microcavity during frequency tuning with an appropriate scanning speed and operational parameters. However, due to the excessive loss caused by tuning, the soliton eventually evolves into a DC distribution. The influence of different parameters on the light field after formation of the soliton is also studied. Other different parameters lead to different distributional forms of soliton evolution. For maintenance of the single soliton, the appropriate detuning parameter and pump power are changed suddenly after the soliton is generated, causing the soliton to remain stable. Moreover, in the single soliton region, a path within the parameter space of detuning and pump power is planned in order to compress the pulse width of the soliton, and the comb spectrum is broadened. The results of theoretical analysis are important for studying field and spectral characteristics during frequency detuning and for maintaining the temporal soliton in the microcavity. [ABSTRACT FROM AUTHOR]

Photosynthesis is one the most important biological processes on earth, producing life-giving oxygen, and is the basis for a large variety of plant products. Measurable properties of photosynthesis provide information about its biophysical state, and in turn, the physiological conditions of a photoautotrophic organism. For instance, the chlorophyll fluorescence intensity of an intact photosystem is not constant as in the case of a single fluorescent dye in solution but shows temporal changes related to the quantum yield of the photosystem. Commercial photosystem analyzers already use the fluorescence kinetics characteristics of photosystems to infer the viability of organisms under investigation. Here, we provide a novel approach based on an optical Fabry–Pérot microcavity that enables the readout of photosynthetic properties and activity for an individual cyanobacterium. This approach offers a completely new dimension of information, which would normally be lost due to averaging in ensemble measurements obtained from a large population of bacteria.

The investigation of optical microcavity solitons is in demand both for applications and basic science. Despite the tremendous progress in the study of microresonator solitons, there is still no complete understanding of all features of their nonlinear dynamics in various regimes. Controlling soliton properties is also of great interest. We proposed and investigated experimentally and theoretically a simple and easily reproducible way to generate Raman solitons with controllable spectral width in an anomalous dispersion region in a functionalized silica microsphere with whispering gallery modes (WGMs) driven in a normal dispersion regime. To functionalize the microsphere, coating (TiO2 + graphite powder) was applied at the pole. The coating is used for effective thermalization of the radiation of an auxiliary laser diode launched through the fiber stem holding the microsphere to control detuning of the pump frequency from exact resonance due to the thermo-optical shift of the WGM frequencies. We demonstrated that the thermo-optical control by changing the power of an auxiliary diode makes it possible to switch on/off the generation of Raman solitons and control their spectral width, as well as to switch Raman generation to multimode or single-mode. We also performed a detailed theoretical analysis based on the Raman-modified Lugiato–Lefever equation and explained peculiarities of intracavity nonlinear dynamics of Raman solitons. All experimental and numerically simulated results are in excellent agreement.

Microlasers in near-degenerate supermodes lay the cornerstone for studies of non-Hermitian physics, novel light sources, and advanced sensors. Recent experiments of the stimulated scattering in supermode microcavities reported beating phenomena, interpreted as dual-mode lasing, which, however, contradicts their single-mode nature due to the clamped pump field. Here, we investigate the supermode Raman laser in a whispering-gallery microcavity and demonstrate experimentally its single-mode lasing behavior with a side-mode suppression ratio (SMSR) up to 37 dB, despite the emergence of near-degenerate supermodes by the backscattering between counterpropagating waves. Moreover, the beating signal is recognized as the transient interference during the switching process between the two supermode lasers. Self-injection is exploited to manipulate the lasing supermodes, where the SMSR is further improved by 15 dB and the laser linewidth is below 100 Hz. [ABSTRACT FROM AUTHOR]

Fiber optofluidic laser (FOFL) integrates optical fiber microcavity and microfluidic channel and provides many unique advantages for sensing applications. FOFLs not only inherit the advantages of lasers such as high sensitivity, high signal-to-noise ratio, and narrow linewidth, but also hold the unique features of optical fiber, including ease of integration, high repeatability, and low cost. With the development of new fiber structures and fabrication technologies, FOFLs become an important branch of optical fiber sensors, especially for application in biochemical detection. In this paper, the recent progress on FOFL is reviewed. We focuse mainly on the optical fiber resonators, gain medium, and the emerging sensing applications. The prospects for FOFL are also discussed. We believe that the FOFL sensor provides a promising technology for biomedical analysis and environmental monitoring. [ABSTRACT FROM AUTHOR]

Multiplexed biomarker detection is highly desirable for the early diagnosis and treatment of diseases. Optofluidic laser has shown extraordinary ability in single biomarker detection, but the simultaneous detection of multiple biomarkers remains unexplored. Here, we develop optofluidic laser immunosensors based on multidimensional division multiplexing technologies. Time division multiplexing (TDM) based optofluidic lasers are demonstrated by the temporal control of the immunoreaction and sequential generation of immunocomplexes. Spatial/wavelength division multiplexing (SDM/WDM) based optofluidic lasers are achieved by integrating microfluidic channels and exploiting different emission bands. The feasibility of the multiplexed laser immunosensors is demonstrated by the detection of dual-biomarkers of acute myocardial infarction and lung cancer. The multiplexed laser immunosensor features the superimposed enhancement effects of laser amplification and latex particles, enabling a limit of detection down to the fM (10−15 molar) level. The assay time can be shortened to 15 min thanks to the utilization of homogeneous immunoreaction. Based on the multiplexed detection of biomarkers, our technology takes a significant step toward the early diagnosis of major diseases. • Latex-enhanced optofluidic laser immunosensor is developed to achieve ultra-sensitive biodetection. • TDM-OFL immunosensor is achieved by the temporal control of generation of immunocomplexes. • SDM/WDM-OFL immunosensor is demonstrated by integrating microfluidic channels and exploiting different emission bands. • The multiplexed immunosensor performs multi-biomarker sensitive detection within 25 min. [ABSTRACT FROM AUTHOR]

On-chip Si3N4 microcavities composed of multi-mode waveguides can achieve high-quality factor and anomalous dispersion simultaneously, which is necessary for solitons generation. It has been proven to be a promising platform for compact optical (Kerr) frequency comb generation. To further reduce the threshold power for generating a single soliton microcomb, a racetrack Si3N4 microcavity with Euler bends is reported. Compared with traditional racetrack microcavities, Euler bending can significantly suppress the sudden change in bending radius at the waveguide connection, which suppresses mode interactions and reduces propagation losses, resulting in an increase in Q factor value. Based on this racetrack microcavity, using the auxiliary laser heating method, a single soliton frequency comb with a repetition rate of 34 GHz and a 3 dB bandwidth exceeding 18 nm (corresponding to a pulse duration of 143 fs) can be generated using only a 19 mW pump laser (estimated on-chip pump power below 10 mW). The optimized racetrack microcavities can be building blocks for integrated photonics systems. [ABSTRACT FROM AUTHOR]

In this paper, the boundary rounding effects of two types of non-circular GaN microcavity system are numerically simulated by the finite element method. When the rounding parameter s of the hexagonal microcavity decreases, the six corners of the regular hexagon are gradually rounded, the results show that the optical mode gradually changes from the hexagonal whispering-gallery mode (WGM) to the perfect circular WGM, and the quality factor of the modes increases correspondingly. For the oval microcavity, the structure parameter δ increases from 0 to 1 when the oval microcavity gradually changes from a stadium cavity to a circular cavity. The simulation results show that the quality factor increases with δ , and the optical mode changes from high-leak mode to WGM. Our results demonstrate the effect of the boundary rounding on the mode pattern and quality factor in hexagonal and oval microcavities. [ABSTRACT FROM AUTHOR]

Both photons and semiconductor quantum-dot (QD) spins are promising candidates for quantum information science and technology. It is of critical significance to realize high-fidelity quantum controlled gates on photon-spin hybrid systems. In this paper, based on the novel balance condition for the interaction between a single input photon and a singly charged QD embedded in an optical single-sided microcavity, we present three schemes for implementing three universal quantum controlled gates, i.e., the two-qubit controlled-NOT (CNOT) gate, the three-qubit Toffoli gate, and the three-qubit Fredkin gate, on composite hybrid quantum systems consisting of flying photons and QD-confined electron spins. By exploiting the balance condition, the noise caused by the unbalanced reflectance of the coupled and uncoupled QD-cavity systems can be efficiently suppressed, so that the fidelity of each quantum gate operation can be raised to unity in principle. The balance condition can be met without the strict requirement of strong coupling, making the high-fidelity quantum gates easier to be demonstrated in experiments. These features can improve the fidelity and feasibility of these schemes, which can be applied to large-scaled quantum computing and quantum information networks. [ABSTRACT FROM AUTHOR]

We report a construction of distributed-feedback (DFB) optical microcavities, which is realized through mechanical contact between a high-quality planar thin film of a polymeric semiconductor and a large-area homogeneous nanograting. Using poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3] thiadiazol-4,8-diyl)] (F8BT) as the active medium for the planar layer, we achieve strong amplified spontaneous emission from such a microcavity with a low threshold. This not only simplifies largely the fabrication techniques for DFB microcavities, but also avoids the unexpected chemical interactions during solution processing between the organic semiconductors and the nanograting materials. Furthermore, high-quality polymer thin films with high surface smoothness and high thickness homogeneity are employed without any modulations for constructing the microcavities. This also suggests new designs of microcavity light-emitting diodes, or even for realizing electrically pumped polymer lasers, simply by metallizing the dielectric nanogratings as the electrodes.

Photonic hyperentanglement, which involves photons simultaneously entangled in more than one degree of freedom (DOF), has many important applications in quantum information processing, especially in high-capacity quantum communications. Interestingly, single-photon qubits encoded in the time-bin DOF are robust for long-distance transmissions in noisy channels. In this paper, we present a hyperentangled-Bell-state generation (HBSG) scheme for preparing two-photon six-qubit states which are simultaneously entangled in the polarization, spatial-mode, and time-bin DOFs. Compared with previous HBSG schemes, we construct an error-detected circuit unit with a quantum-dot (QD) spin in a double-sided optical microcavity, with which errors due to imperfect interactions between photons and QD systems can be easily detected, so that the error-detected circuit unit can relax the experimental requirement and improve the fidelity of our scheme largely. Meanwhile, our scheme is used to prepare two-photon hyperentangled states in polarization-spatial-time three DOFs, which is significant for faithful entanglement distribution and quantum repeater. These features make our scheme more feasible and useful in high-capacity and long-distance quantum communications with hyperentanglement. [ABSTRACT FROM AUTHOR]