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Photon blockade is a single-photon generation method based on strong nonlinearities. In this Letter, we propose a system with emission and pumping modes to realize photon blockade by a microring resonator-waveguide system. We find that Friedrich-Wintgen bound states in the continuum (BICs) emerge from destructive quantum interference by engineering complex dissipation coupling. Consequently, photon blockade can be observed due to the high quality factor of one BIC eigenmode and the reduction of effective decay when the Friedrich-Wintgen condition is satisfied. Moreover, we show that photon blockade can also occur at a small Kerr nonlinearity. We also investigate the influences of phase and strength in dissipation coupling on photon blockade.
Two-photon vision enables perception of near-infrared light through nonlinear absorption in retinal photopigments, showing a quadratic dependency on laser intensity. We measured two- and one-photon visual thresholds for varying beam diameters (with effective NA = 0.02-0.09) and defocus levels under dark- and light-adapted conditions. Two-photon visual thresholds varied significantly with beam diameter for stimuli focused on the retina and showed greater sensitivity to defocus than one-photon thresholds, especially at larger NA. While defocus blurs visible stimuli, in two-photon vision, it mainly decreases retinal photon density, reducing brightness without image degradation. These results emphasize, for the first time, to the best of our knowledge, the importance of beam diameter, focus quality, and accurate defocus correction in optimizing two-photon--based visual displays.
When a photon traverses a cloud of atoms without scattering, how much time does it spend as an atomic excitation? To address this question, we used the cross-Kerr effect to weakly probe the degree of atomic excitation caused by a transmitted resonant "signal" photon by measuring the phase shift induced on a (separate, off-resonant) "probe" beam, postselected on cases when the signal photon is transmitted. The time integral of this observed phase shift, properly normalized and averaged over many runs in which the photon is detected after transmission, is the excitation time of interest, in a weak-valued sense. We measured mean atomic excitation times ranging from (-0.82±0.31)τ_{0} for the most narrow band pulse to (0.54±0.28)τ_{0} for the most broadband signal pulse, where τ_{0} is the non-post-selected excitation time, given by the scattering probability multiplied by the atomic lifetime τ_{sp}. Across a range of pulse durations and optical depths, our results are consistent with the recent theoretical prediction that the weak value of the atomic excitation time caused by a transmitted photon equals the group delay experienced by the light. Our experimental results show that negative times are not limited to describing the shift in the peak of a reshaped wave packet (as resulting from group delay), but they also provide the appropriate description of the weak-valued time the photon spends as an atomic excitation.
Programmable photonic networks carry out universal unitary functions by independently operating on the amplitude and phase of guided light. Exploiting the reconfigurability and spatiospectral degrees of freedom of these systems, the majority of state-of-the-art photonics applications, ranging from microwave photonics to photonic computing and optical communication links, can be demonstrated in one unified system. Existing techniques require a large footprint due to weak modulation efficiency, and continuous power dissipation to maintain the configured state. Here, we demonstrate a programmable recirculating mesh unit cell based on the nonvolatile low-loss phase-change material Sb2Se3. The demonstrated devices achieve an ultrashort active length (<10 μm, more than 15 times smaller than the current state of the art of competing technologies) and zero static power, in combination with high-extinction switching (>20 dB), broadband operation (>15 nm), and low insertion loss (<2 dB). This work forms the basis for nonvolatile field-programmable coupler arrays (nv-FPCAs) and zero-static power reconfigurable optical interconnects.
The investigation of neural circuit dynamics faces a fundamental challenge: existing tools cannot simultaneously achieve cellular resolution, millimeter-depth penetration, and compatibility with freely behaving subjects. Electrophysiology offers temporal precision at depth, while advanced microscopy provides superb resolution, but is physically constrained to superficial layers or head-fixed preparations. In this review, we propose that implantable photonic devices are emerging as the critical solution to address this challenge. We first critically examine the evolution of electrophysiology and microscopic imaging, establishing their inherent trade-offs. We then detail how integrated photonic probes, leveraging semiconductor innovations like single-photon avalanche diode (SPAD) arrays and µLEDs, enable optical sensing and manipulation deep within the brain of behaving animals. By establishing frameworks to compare important performance and synthesizing the latest research, we provide analysis of this transformative shift. Finally, we outline the multidisciplinary challenges in scaling, thermal management, data processing, and biocompatibility, which must be overcome to realize the full potential of implantable photonics as a new paradigm for closed-loop neuroscience and clinical translation.
X-rays play an essential role in modern tumor radiotherapy. Precise X-ray dosimetry is crucial for tumor radiotherapy to maximize therapeutic efficacy while minimizing normal tissue damage. Compared to traditional X-ray physical dosimeters, hydrogels are strong candidates for detecting X-ray doses due to their excellent tissue equivalence, ease of chemical modification, tunable sizes and low costs. However, most of these sensors are time-consuming, dose rate dependent, and irreversible. Additionally, they require sophisticated device readout systems and skilled personnel. To overcome these shortcomings, this study focuses on developing a hydrogel photonic material that is capable of sensing X-rays. In this paper, we first synthesize a series of poly(N-isopropylacrylamide-co-vinylferrocene) microgels (PVFc MG) with a variety of microstructures by modulating chemical compositions and synthetic strategies. Subsequently, Au-PVFc MG-Au photonic interferometers are generated by sandwiching PVFc MG monolayer between two Au metal layers. After depositing the X-ray-irradiated Fe2+ solution, the optical signals of the Au-PVFc MG-Au interferometer redshift due to the swelling of the microgel. As a result, the optimized interferometer exhibits a fast and linear response in the dose range of 0.1-20 Gy, a sensitivity of ∼4 nm/Gy, 95% of accuracy and dose-rate independence (0.847-5.085 Gy/min). It can return to its initial state in the presence of ascorbic acid, showing excellent reversible sensing capability. This work provides a promising platform for precise clinical X-ray dose monitoring in radiotherapy. This study explores the use of vinylferrocene microgel-based photonic interferometers for detecting clinical X-ray doses. The sensing capabilities of the Au-PVFc MG-Au interferometers can be enhanced by modifying the chemical compositions and structures of the microgels. The underlying response mechanism is examined in detail. When applied in clinical X-ray dose sensing, these interferometers demonstrate exceptional performance, surpassing previous reports in terms of response time, linear responsivity, accuracy, reversibility, and dose rate independence.
Flat photonic bands enable enhanced light-matter interaction but are often accompanied by increased radiative loss or strong angular sensitivity, limiting their practical utility. We report a photonic crystal (PhC) slab combining extreme band flatness with normal-incidence high-Q resonances through two physically cooperative mechanisms. Through effective mass engineering near the Γ point, we realize an ultra-flat dispersion with a relative variation as low as Δλ/λ ≈ 2.4 × 10-4, creating a momentum-robust optical mode. Independently, accidental bound states in the continuum (BICs) are manipulated to merge at the zone center, yielding Q-factors exceeding 108. The distinct behaviors of these degenerate modes enable a self-referenced sensing scheme with intrinsic stability against thermal perturbations. This work establishes a unified approach to decoupling dispersion flattening and radiation suppression in planar photonics.
Stimuli-responsive materials are pivotal for advanced photonics, yet achieving ones with multiple-dimensional manipulation and high robustness remains a challenge. Here, we present a shape-memory chiral photonic platform with multi-stimuli-responsiveness by sophisticatedly controlling the crosslinking chemistry and density of a triplet-triplet annihilation upconversion featured cholesteric elastomer. A thermally resettable shape memory effect on structural colors is induced by force in the elastomer with an oligomer-lowered crosslinking density, which also exhibits exceptional stretchability and enhanced optics, a remarkable 259 nm blueshift over 215% strain. The covalent incorporation of annihilators secures homogeneity and stability of the system. The material possesses programmable optical properties, including chirally, thermally, and mechanically regulated structural colors and photoactivated luminescence, enabling high-dimensional information encryption with accessibility to scalable spray-printing. This work provides a versatile material strategy for cutting-edge optical encryption and paves the way for next-generation wearable sensors, adaptive optical devices, and interactive camouflage technologies.
Ensuring signal fidelity and output stability against electrical noise is a central challenge for optoelectronic sensing-computing systems. However, conventional optoelectronic devices often suffer from output instability due to input voltage fluctuations. This limitation hinders the realization of multifunctional logic operations with high interference immunity in a single device. Here, we propose a photon-assisted Fowler-Nordheim tunneling regulator based on a SnS2/WSe2 van der Waals heterostructure. Through a gate-activated, light-programming strategy, the device achieves a voltage-immune constant current output. Leveraging these intrinsic physical properties, reconfigurable logic units were constructed. The NOT logic gate achieves a switching ratio of up to 104, while the robust NAND logic gate exhibits remarkable noise immunity (coefficient of variation, CV ∼ 1%), effectively filtering noise jitter from input signals to ensure precise logic output. This work applies the photon-assisted tunneling effect to both analog signal conditioning and digital logic operations, highlighting the immense potential of light as a programming tool for quantum transport processes and providing a distinct device prototype for the development of interference-resistant and multimodal integrated on-chip optoelectronic systems.
Achieving strong light-matter interaction to manipulate emission requires integrating colloidal perovskite quantum dots (PQDs) with plasmonic nanocavities, yet this integration is challenged by their vulnerability to polar solvents. We successfully synthesized highly emissive, solvent-resistant CsPbI3 PQDs and integrated them into nanoparticle-on-mirror structures. This integration enabled a 435-fold reduction in emission lifetime and a 250-fold increase in total emission intensity. Key results include a very short radiative lifetime below 12 picoseconds and a record-high single-photon emission rate exceeding 2.3 × 109 counts per second at room temperature. Notably, we also observed nonblinking single-photon emission with high purity arising from nanocavity-enhanced radiative electron-hole recombination. Finite-difference time-domain simulations confirmed ultrasmall mode volumes of ~3 × 10-5 (λ/n)3, effectively enhancing spontaneous emission via the Purcell effect. These ultrabright and nonblinking properties highlight the strong potential of this platform for future quantum technology applications.
Ultra-low linewidth widely tunable lasers capable of emission by design from the visible to shortwave infrared are important building blocks for a range of precision applications including quantum sensing and computing, timekeeping, metrology, optical clocks, and fiber sensing. Importantly, integration of precision tunable lasers in a CMOS foundry compatible platform that can support higher level integration with other components, such as low loss silicon nitride (Si3N4), is an important step towards full system on chip solutions. Integration of the III-V gain material with the Si3N4 tunable cavity is a critical step towards this goal and must be achieved through a low-cost, manufacturable, and reliable process. However, this co-integration has remained challenging due to tight alignment tolerances and mode mismatches between the semiconductor and silicon nitride waveguides. 3D-printed photonic wire bonding (PWB) offers a robust approach to hybrid integration due to the relaxation of waveguide alignment tolerances and the inherent low-loss mode matching. In this work, we demonstrate a narrow linewidth PWB-integrated Si3N4 external cavity tunable laser (ECTL) with a 3.75-7.77 Hz fundamental linewidth measured across a 60 nm tuning range and a 1.27 kHz integral linewidth: a reduction of nearly three orders of magnitude in fundamental linewidth compared with previously reported PWB-integrated ECTLs in Si3N4. The PWB process has the potential to realize reliable and manufacturable tunable lasers on-chip with the performance of table-top fiber lasers. These results establish photonic wirebonding as a viable integration pathway for precision photonic systems, enabling portable, scalable, and cost-effective solutions for quantum, low-noise microwave, and sensing applications.
Integrated optics is primarily based on planar designs due to the availability of mature lithographic manufacturing and optical confinement constraints. These 2D designs with finite thickness in the third dimension are often referred to as 2.5D. Full 3D photonic architectures, with refractive-index variations along the three dimensions, hold the promise of higher integration density and novel, to the best of our knowledge, light control capabilities, but require advanced multi-layer stacking techniques with precise alignment and planarization. Nanoscale 3D printing techniques, such as multi-photon lithography, can address these challenges, and are gaining momentum thanks to their cost-effectiveness and rapid prototyping capabilities compared to silicon foundries. Despite this potential, the exploration of freeform polymer optics at the nanoscale remains limited due to challenges associated with low-index materials and a lack of design tools. Here, we address these limitations by applying a multi-layered inverse design approach for polymer-based integrated optics. We systematically compare 3D with 2.5D designs (all simulations are conducted in 3D), for the task of demultiplexing two wavelengths with spectral spacing from 100 nm to 20 nm. Our numerical results show that fully 3D polymer designs consistently outperform their 2.5D counterparts, achieving higher efficiencies at equal footprint. These findings propel the advancement of a next generation of miniaturized 3D devices for polymer-based integrated optics.
We propose and demonstrate a proof-of-concept hybrid photonic-digital neural network that exploits optical frequency comb lines and their second-order nonlinear interactions for both classification and image generation. In this architecture, input features are encoded in the amplitudes of individual comb lines, while their relative phases serve as trainable parameters. For classification, it achieves ∼98% average accuracy on a 40-sample make-moons dataset, with the mean square error reduced from 0.7 to 0.05 post-training. For image generation, a conditional variational autoencoder is implemented using a small dataset of 18 MNIST digits over 3 categories, generating new digits with a reconstruction loss of 0.75. These results establish the feasibility of combining frequency comb lines and nonlinear optics for both discriminative and generative neural network tasks.
Although Rydberg atoms have shown promise for use in novel types of radio frequency (rf) receivers, they have generally not been considered phase sensitive without the use of closed-loop interferometry or auxiliary rf fields. Here, we show that the high coherency of a narrow-linewidth three-photon ladder excitation scheme unique to cesium atoms enables all-optical sensing of transient changes in rf phase within a room temperature vapor cell. The transient response on the probe laser's transmission originates from phase-to-amplitude conversion via a disturbance of the coherency of the system in response to the phase shift of the rf field. We show that the amplitude and frequency of the oscillatory response provide information on the magnitude and direction of any rf field detuning. We demonstrate that the detuning sensitivity can be used to identify Doppler shifts in radar applications, by applying phase shifts embedded in rf pulses. The phase modulation within the radar pulse acts as a form of compression that facilitates the simultaneous detection of both target position and velocity.
We study photonic meta-atoms, a unique class of composite solitary wave supported in nonlinear waveguides. We establish an analogy to one-dimensional soft-core atoms, allowing us to describe the complex dynamics via concepts from atomic physics. Higher-order dispersive effects cause specific spectral resonances characteristic for the eigenspectrum of a meta-atom. We demonstrate that subtle changes in this level of spectrum cause frequency shifts of the resonances. These shifts consist of isotopic and isomeric contributions that can be distinguished in terms of a simple model. We further demonstrate a generic mechanism that causes a Zeeman-like splitting of resonance lines.
Simultaneously achieving giant chirality, high-efficiency nonlinearity, and robust nonreciprocity remains elusive due to the inherent trade-off between the structural asymmetry required for chiroptics and the high quality (Q) factors essential for nonlinearity. Here, we overcome this fundamental limitation in silicon metasurfaces by exploiting symmetry-protected bound states in the continuum (BICs). By implementing a two-stage symmetry-breaking mechanism that combines an in-plane structural rotation with out-of-plane height perturbations, we engineer high-Q (104) resonances dominated by magnetic quadrupole modes. Linearly, the device exhibits robust asymmetric transmission with a forward circular dichroism (CD) of 0.98 and a backward CD of -0.79. Leveraging intense near-field confinement, we realize third- and fifth-harmonic generation efficiencies of 3.6 × 10-3 and 2.9 × 10-9 at a moderate pump intensity of 1 MW/cm2. Crucially, the chiral-nonlinear coupling enables perfect nonlinear nonreciprocity, yielding near-unity nonlinear CD values of ±0.99. This work establishes a compact paradigm for high-performance chiral nonlinear isolators.
Non-volatile optical switches are key components in programmable photonic integrated circuits. Here, we propose a 2×2 photonic switch based on an Sb2S3-embedded multimode interference waveguide crossing. The device routes light between reflection and transmission paths via Sb2S3 phase transitions facilitated by total internal reflection. Subwavelength tooth structures are incorporated on the reflecting facets to engineer the optical field distribution via the gradient-index effect. The device achieves an insertion loss of 0.61 dB and exhibits low crosstalk below -21 dB over a 300-nm bandwidth. Fabrication tolerances are evaluated through structural variations, indicating stable operation. In addition, multi-level tuning of the power splitting ratio is achieved, suggesting potential applications in reconfigurable photonic signal processing.
Resonance fluorescence arises from the coherent interaction of laser light with a two-level system and constitutes a quantum light source exhibiting single-photon emission and antibunching, making it a fundamental building block for future quantum networks. Our recent work [Nat. Commun.16, 6453 (2025)10.1038/s41467-025-61884-x] demonstrates that under continuous-wave excitation and in the absence of pure dephasing, the single-time joint state of resonance fluorescence and the two-level system can be described by a pure entangled state. Here, we analyze the cross-correlation and auto-correlation properties of the quantum optical field generated by the interference of resonance fluorescence with laser light at the resonance excitation frequency. Simulation results indicate that by varying the intensity or phase of the interfering laser light, the higher-order coherence of the post-interference quantum optical field transitions from anti-bunching to super-bunching behavior, consistent with recent theoretical and experimental advances by mean-field engineering. This approach offers a complementary framework to characterize and manipulate the multiphoton quantum optical fields.
Breaking the fundamental distance limit of dipole-dipole interactions is key to enabling scalable quantum and photonic technologies. Conventional nonradiative energy transfer [Förster resonance energy transfer (FRET)] is intrinsically confined to deep subwavelength distances, limiting its scalability. Here, we demonstrate millimeter-scale, coherent dipole-dipole energy transfer enabled by nonradiative bound states in the continuum (BICs) in a gold metasurface. Using a custom terahertz near-field time-domain microscope with dipolar emitter-detector probes, we observe strongly anisotropic energy transfer enhanced along one axis, where BIC modes establish long-range spatiotemporal coherence, and suppressed along the orthogonal axis. By systematically reducing the array size, we reveal that energy transfer efficiency and spatiotemporal coherence are maximized near the metasurface's center, where boundary-induced scattering is minimized. These findings establish BICs and quasi-BICs as robust, nonradiative channels for extended, directional, and coherence-preserving dipolar interactions, providing a versatile platform for quantum communication, integrated nanophotonics, and biosensing technologies.
A new scheme for detecting wavelike dark matter (DM) using Rydberg atoms is proposed. Recent advances in trapping and manipulating Rydberg atoms make it possible to use Rydberg atoms trapped in optical tweezer arrays for DM detection. We propose to prepare a large ensemble of Rydberg atoms and to observe the excitations between Rydberg states by the DM-induced effective electric field. A scan over DM mass is enabled with the use of the Zeeman and diamagnetic shifts of energy levels under an applied external magnetic field. Taking dark-photon DM as an example, we demonstrate that our proposed experiment can have high enough sensitivity to probe previously unexplored regions of the parameter space of dark-photon coupling strengths and masses.