Fiber-optic sensing technology has the advantages of passivity, anti-electromagnetic interference, long-distance measurement, high sensitivity and high accuracy, small size, and adaptability to harsh environments such as high-vacuum, high-pressure, and strong magnetic fields compared with the traditional electrical sensing technology. However, with the increasing application requirements, how to further improve the sensitivity of fiber-optic sensors, extend the detection limit and improve the maintenance-free capability has become one of the core issues of the current research. This paper reviews the principle, preparation, and application of fiber-optic microstructured sensing based on abrupt field type. It specifically outlines the development and applications of micro-nano optical fibers, photonic crystal optical fibers, optical fiber gratings and structured optical fibers, and lists the main preparation methods of two types of micro-nano optical fibers from the basic theory of optical fiber microstructured sensor devices.
C. Abinash Bhuyan, Anil K. Chaudhary, Kishore K. Madapu
et al.
For designing an efficient terahertz (THz) emitter, the defect density of the semiconductors is smartly increased to reduce carrier lifetime, which subsequently lowers the overall power output of the semiconductor. To overcome this fundamental trade‐off, this study presents a novel approach by integrating a direct bandgap 2D semiconductor, such as monolayer MoS2 (1L‐MoS2) with a well‐known THz emitter and low‐temperature‐grown gallium arsenide (GaAs). The fabricated hybrid 2D/3D vertical van der Waals heterostructure shows a 15% higher THz emission compared to bare GaAs due to phase‐coherent addition of second‐order nonlinear susceptibility, and overall enhancement in the electric field of the laser. The photoluminescence (PL) enhancement factor of 2.38 in heterostructures at GaAs emission energy of 1.42 eV. However, the substantial quenching of PL emission for 1L‐MoS2 at the energy of 1.84 eV is attributed to the Dexter‐type exciton transfer mechanism at type‐I band alignment. THz time‐domain spectroscopy reveals a significant increase in optoelectronic properties, such as optical conductivity becoming doubled, and a 50% reduction in absorption coefficients. The study introduces a new route for fabricating large‐area and compact mixed‐dimensional van der Waals heterostructures, which can be used to enhance the efficiency of conventional semiconductor technologies and THz‐based optoelectronic devices.
Md. Iquebal Hossain Patwary, Tahir Bashir, Akito Iguchi
et al.
The sub-wavelength grating NRD guide (SWG-NRD guide) can transmit the single LSM<inline-formula><tex-math notation="LaTeX">$_{01}$</tex-math></inline-formula> mode regardless of arbitrary bends without exciting the LSE<inline-formula><tex-math notation="LaTeX">$_{01}$</tex-math></inline-formula> mode, unlike the standard NRD guide, making it a promising candidate in developing THz-wave integrated circuits. The simple bending waveguides and power-splitting devices with sharp curvature have been previously investigated on this platform; however, more sophisticated devices with arbitrary bends have yet to be thoroughly examined. This paper presents the design of a SWG-NRD 3-dB wavelength-insensitive coupler (WINC) based on Mach-Zehnder interferometer (MZI) with arbitrary bends, utilizing the topology-optimized matching circuit. The WINC achieves a broadband operational range from 0.93 THz to 1.06 THz with an imbalance of less than <inline-formula><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 0.5 dB and an average coupling ratio of 49.2%. The average return loss and isolation are better than <inline-formula><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 21 dB and <inline-formula><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 24 dB, respectively, and the average insertion loss is only 0.089 dB. To demonstrate the usefulness of the WINC, a design of an MZI interleaver is presented. The tolerance for fabrication errors in the proposed devices is also thoroughly discussed. The designed devices do not experience LSE<inline-formula><tex-math notation="LaTeX">$_{01}$</tex-math></inline-formula> mode excitation at the bends, confirming the platform's relevance and devices' possible application in THz integrated wavelength-division multiplexing (WDM) systems.
Monolayer 2D semiconductors, such as WS2, exhibit uniquely strong light-matter interactions due to exciton resonances that enable atomically-thin optical elements. Similar to geometry-dependent plasmon and Mie resonances, these intrinsic material resonances offer coherent and tunable light scattering. Thus far, the impact of the excitons temporal dynamics on the performance of such excitonic metasurfaces remains unexplored. Here, we show how the excitonic decay rates dictate the focusing efficiency of an atomically-thin lens carved directly out of exfoliated monolayer WS2. By isolating the coherent exciton radiation from the incoherent background in the focus of the lens, we obtain a direct measure of the role of exciton radiation in wavefront shaping. Furthermore, we investigate the influence of exciton-phonon scattering by characterizing the focusing efficiency as a function of temperature, demonstrating an increased optical efficiency at cryogenic temperatures. Our results provide valuable insights in the role of excitonic light scattering in 2D nanophotonic devices.
Hadrian Bezuidenhout, Cade Peters, Ram Kumar
et al.
Optical Skyrmions are topological forms of structured light with the potential of an infinite encoding alphabet that is immune to disturbance. This attractive prospect is hindered by the lack of any topological detector, a challenging problem due to the non-orthogonal nature of the topological invariant (N). Here we demonstrate the first deterministic detector for Skyrmionic topologies of light using a deep diffractive optical neural network. Our network uses two independent processing channels of 5 diffractive layers each to map incoming topologies to spatially separated Gaussian channels from which N can be detected. We overcome the complexity of the training by using a spatial mode basis rather than pixels, reducing the training variables by x1000 compared to current methods. We use the detector on an input set of 81 input topologies, showing high accuracy even in the presence of significant levels of noise. Finally, to show the practical utility of the device, we transmit and receive an image encoded in a 14-level topological alphabet with no discernible cross-talk. Our work offers a new paradigm for the emergent field of diffractive optical networks and can easily be extended to other forms of optical topologies, setting a clear pathway for their deployment in real-world applications.
Aryan Bhardwaj, Debanuj Chatterjee, Ashutosh Kumar Singh
et al.
We report an all-fiber-based experimental setup to generate a correlated photon-pair comb using Four Wave Mixing (FWM) in Highly non-linear fiber (HNLF). Temporal correlations of the generated photons were confirmed through coincidence measurements. We observed a maximum of 32 kcps, with a coincidence to accidental ratio of <inline-formula><tex-math notation="LaTeX">$17 \pm 1$</tex-math></inline-formula>. To further understand the underlying processes, we also simulated a generalized FWM event involving the interaction between an arbitrary frequency comb and a Continuous Wave (CW) pump. non-linear dynamics through the HNLF were modelled using Schrödinger propagation equations, with numerical predictions agreeing with our experimental results.
Bioluminescent tomography (BLT) is a noninvasive imaging technology that uses optical methods to study physiological and pathological processes at the cellular and molecular levels. It is a powerful tool for early diagnosis and treatment of tumors, as well as drug development. However, the simplified optical transmission models and the ill-posed inverse reconstruction limit its wide applications. The development of deep learning has provided new potential for extending the applications of optical BLT. Researchers have introduced various methods such as neural networks and self-attention mechanisms to improve reconstruction accuracy. Despite these efforts, weak energy points around the reconstructed light source center still impact the accuracy of restoration. In this study, we propose a dual-branch network based on a combination of attention mechanism and fully connected layers (FC-AM) to reduce centroid error and improve reconstruction performance. The network architecture consists of a fully connected (FC) subnetwork and an attention mechanism-based dual-branch (AMDB) subnetwork. The FC subnetwork is used to process input data. AMDB subnetwork is used for deep feature extraction, and captures feature information from different perspectives in parallel. Each branch of the AMDB subnetwork is composed of four AM subnets, which extract features through multilayer linear transformations and attention mechanisms. The outputs of the AMDB are combined through feature fusion to produce the final result. Numerical simulations and experimental results demonstrate that the FC-AM network significantly improves BLT reconstruction performance compared to existing methods (KNN_LC and AMLC networks), offering enhanced stability and accuracy.
This article theoretically proposes a multi-layer Fabry-Perot cavity structure based on nonlinear MoS2, whose cavity is composed of asymmetric photonic crystals. In this structure, we observed a low threshold optical bistability phenomenon on the order of a in the visible light band, which is caused by the large third-order nonlinear conductivity of the bilayer MoS2 and the Fabry-Perot cavity resonance. Research has found that when light is incident from two different directions in an asymmetric Fabry-Perot cavity, the optical bistability exhibits not exactly the same behavior. In addition, we further investigated and found that the optical bistability behavior in this simple multi-layer structure is closely related to parameters such as incident wavelength, Fabry-Perot cavity length, and refractive index of the photonic crystal dielectric. This work provides a new approach for the implementation of low threshold optical bistable devices in the visible light band, which is expected to be applied in nonlinear optical fields such as all optical switches and all optical logic devices.
Soheil Khajavi, Ali Eghrari, Zahra Shaterzadeh-Yazdi
et al.
Scattering scanning near-field optical microscopy (s-SNOM) is a technique to enhance the spatial resolution, and when combined by Fourier transform spectroscopy it can provide spectroscopic information with high spatial resolution. This paper studies two analytical models for the s-SNOM probe using atomic force microscopy (AFM) tip and its interaction with a dielectric material. We evaluate the validity of these models by retrieving the permittivity spectrum of a sample material through an inverse method.
Anthony A. Song, Mason T. Chen, Taylor L. Bobrow
et al.
We introduce a compact, two-camera laparoscope that combines active stereo depth estimation and speckle-illumination spatial frequency domain imaging (si-SFDI) to map profile-corrected, pixel-level absorption and reduced scattering optical properties in tissues with complex geometries. Our approach uses multimode fiber-coupled laser illumination to generate high-contrast speckle patterns, requiring only two images for optical property estimation. We demonstrate 3D profilometry using active stereo from low-coherence RGB laser flood illumination, which corrects for measured intensity variations caused by object height and surface angle differences. Validation against conventional SFDI in phantoms and an in-vivo human finger study showed good agreement, with profile-correction improving accuracy for complex geometries. This stereo-laparoscopic implementation of si-SFDI provides a simple method to obtain accurate optical property maps through a laparoscope, potentially offering quantitative endogenous contrast for minimally invasive surgical guidance.
Precisely capturing and manipulating microparticles is the key to exploring microscopic mysteries. Optical tweezers play a crucial role in facilitating these tasks. However, existing optical tweezers are limited by their dependence on specific beam modes, which restrict their ability to flexibly switch and manipulate optical traps, thereby limiting their application in complex scientific challenges. Here, we propose a new method to achieve type switching and manipulation of optical traps using a single structured beam via optical coherence engineering. A conjugate-model random structured beam with a switch is designed. By altering the state of the switch, we can change the type of optical cage, enabling the capture of different particle types. Furthermore, the range, strength, and position of the optical trap can be controlled by adjusting the initial beam parameters. We hope that optical coherence engineering will extend the capabilities of existing structured optical tweezers, paving the way for advances in future optical tweezers applications.
Hollow-core anti-resonant optical fiber (HC-ARF) provides solutions for breaking the bottlenecks in areas of high-power transmission and high-efficiency optical waveguide. Other than transporting light wave, HC-ARFs can synergistically combine microfluidics and optics in a single fiber with unprecedented light path length not readily achievable by planar optofluidic configurations. The unique features of strict light confinement, wide transmission band and low transmission loss of HC-ARFs enable high sensing performance with low sample consumption, outcompeting conventional optical assays. In this review, we provide a comprehensive overview of HC-ARFs for label-free molecular sensing. We deliver information on the light propagation mechanism and state-of-the-art structures of HC-ARFs, as well as recent progress in chemical and biomedical sensing mainly covering gas, liquid, DNA and protein sensors along with exosome-based liquid biopsy and cancer cell detection. At the end, challenges and prospects of HC-ARF for sensing applications are discussed.
We present a novel implementation of conditional Long Short-Term Memory Recurrent Neural Networks that successfully predict the spectral evolution of a pulse in nonlinear periodically-poled waveguides. The developed networks offer large flexibility by allowing the propagation of optical pulses with ranges of energies and temporal widths in waveguides with different poling periods. The results show very high agreement with the traditional numerical models. Moreover, we are able to use a single network to calculate both the real and imaginary parts of the pulse complex envelope, allowing for successfully retrieving the pulse temporal and spectral evolution using the same network.
Optical anticounterfeiting certifies the authenticity of goods using optical information coding units. A Raman tag with Raman peaks serving as copious optical information coding units is optimal for optical anticounterfeiting. However, complex manufacturing conditions, the use of toxic materials/pollutants, and the request for cross‐reference with fluorescence and/or Rayleigh scattering limit its actual application. Herein, these drawbacks are tackled by proposing the color space‐correlated Raman spectroscopy of diamonds, which are recognized as an extraordinary material in many respects. Specifically, diamond is utilized as a Raman tag because the 1332 cm−1 Raman peaks generate unlimited information coding states with excitation wavelengths and excitation powers. The diamond Raman spectra with excitation wavelength and excitation power in color space and grayscale space to access a 6D (R, G, B, Alpha, excitation wavelength, and excitation power) information coding space are swept. The design's implementation with a diamond is first showcased. Then, the corresponding information coding capacities in grayscale, color space and the dependencies of red, green, blue (RGB) color filters are investigated. Finally, a practical application of the method is proposed. This work opens up a new pathway for publicizing Raman‐based optical anticounterfeiting by an infinitely scalable information coding strategy with diamond photonics.
Ilarion Khromiuk, Nikolai Galunov, Nataliya Karavaeva
et al.
Recently, we have developed a new type of the scintillation material, namely organic composite scintillators. It is a non-scintillating transparent gel composition (a polysiloxane elastomer) containing grains of organic single crystals. The grains are obtained after directional crystallization of the material by crushing a crystalline ingot under a layer of liquid nitrogen. This approach removes technological restrictions on the area of the entrance window of a scintillator, does not require the growth of structurally perfect single crystals and their subsequent mechanical treatment. In contrast to organic single crystals and liquids, these materials are not continuous media but heterostructured ones.The ability of single crystals and liquids to separate signals from radiations with different specific energy losses dE/dx is well known. Due to the peculiarities of the creation and recombination of triplet-excited (T) states in these objects is also well studied. Such information on heterostructured scintillation materials, for which the grain size can limit migration of T-states, is practically absent.We discuss the results of the investigation of the luminescence spectra upon excitation by light into the T-states absorption region and the relative light yield of composite scintillators containing p-terphenyl grains (both activated and non-activated) and trans-stilbene grains. We used the grain fractions from 0.04 to 1.0 mm. We obtained and studied both single-layer samples (the thickness of a sample practically corresponded to the grain size of the scintillation material) and samples of 5 mm thick. The research results showed that samples with grain fractions of less than 0.04, 0.06 and between 0.06 and 0.1 mm have low intensity of the delayed fluorescence and relative light output values. We obtained that to separate radiations with different dE/dx by the shape of the radioluminescence pulse it is advisable to use grain fractions larger than 0.1 mm. We also discuss the physical processes that can lead to such results.
Photonics-assisted microwave instantaneous frequency measurement (IFM) is considered as a promising technique for detecting an unknown radio-frequency (RF) signal, which has advantages of broad frequency measurement range and fast processing speed. Up to date, there is no photonics-assisted IFM system that can essentially measure an unknown RF signal time-frequency information with power fluctuating seriously. Moreover, the measurement accuracy and frequency modulation recognition are not as good as those of traditional electronic methods. Here, we propose an IFM scheme based on the combination of Brillouin gain spectrum (BGS) and Brillouin loss spectrum (BLS), which is RF-power-independent with high measurement efficiency. The combination of BGS and BLS to construct the amplitude comparison function (ACF) can reduce the influence of RF signal power fluctuation within 21.27 dB by single-shot measuring. When an appropriate frequency interval with frequency domain monotonous power of microwave comb signal is modulated on the pump lightwave, the IFM accuracy of the unknown signal reaches about 1 MHz. After the initial calibration of the system, it can recognize the time-frequency variation of single tone signal, linear frequency modulated signal (LFM), nonlinear frequency modulated signal (NLFM), and Costas signal. This scheme will help to promote the application of the IFM in the field of spectrum reconnaissance and reception.
Circularly polarized luminescence (CPL) of chiral materials responsive to external stimuli has drawn widespread attention due to their important applications in smart photonic materials. Here, a CPL‐active chiral emitter derived from guanidine‐substituted 1,8‐naphthalimide (R/S‐1) is reported, which could emit tunable circularly polarized light through regulating the situation of protonation/deprotonation in aqueous, as well as the solvent polarity. Tunable fluorescence emission from the protonated compound can be observed, which is contributed to excited‐state proton transfer of guanidine moiety, as well as the intramolecular charge transfer of naphthalimide group. Subsequently, color‐tunable CPL is obtained, enabling a single‐molecule‐white‐color circularly polarized light emission. Additionally, by introducing R/S‐1 into chiral nematic liquid crystal film, CPL emission is adjusted by exposing to acid/alkaline environment, which can be directly distinguished by naked eyes due to the extremely large dissymmetry factor (|glum| = 1.1). This work opens new venues for photonic applications of CPL active materials.
We design and experimentally demonstrate a radio frequency interference management system with free-space optical communication and photonic signal processing. The system provides real-time interference cancellation in 6 GHz wide bandwidth.