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The dye laser analysis depends on the gain equation that contains cross sections of the relevant emission and absorption molecular transitions involved in the lasing process. The absorption cross-section σs (v) is directly related to the absorbance curves of the dye. The emission cross-section σem (v) has been derived in terms of directly measurable spectroscopic quantities. The low frequency tail of the absorption curves is minutely diminishing for very dilute solutions(~=10-5 mole/lit) usually used in laser system. This low frequency tail overlaps the operating frequency band of the laser. The linear dependence of the dye absorption on the dye concentration (Beer- Lambert law), is used to solve the low frequency tail problem. The intrinsic gain characteristics are calculated for the dye Rhodamine "B" and the results are in good agreement with the rep orted experimental results.

A compact random fiber laser based on a short artificial Rayleigh reflector and heavily-doped Er fibers (custom-made and commercial as a reference) has been proposed, characterized and optimized in terms of efficiency, linewidth and noise level. A 10-cm artificial Rayleigh reflector with mean scattering level of +41.3 dB/mm relative to the natural Rayleigh scattering of the host fiber and low insertion loss level (~0.05 dB/cm at 1535 nm) was fabricated using a femtosecond direct writing technique. Its implementation as a distributed output mirror in a half-open cavity of a 980-nm diode pumped Er-doped fiber laser results in random lasing at 1535 nm in single- and few-mode regimes with power up to 100 mW, slope efficiency up to 16.5%, and signal-to-noise ratio up to 60 dB. A single-frequency regime with ~10 KHz linewidth was observed at output power up to 2.5 mW. Tunability potential of such random lasers is also demonstrated.

Narrow linewidth nonlinear frequency conversion has attracted numerous research attentions. In this manuscript, we demonstrate efficient frequency conversion with weak spectral broadening characteristics through Raman-assisted four-wave mixing (FWM) process in birefringent phosphosilicate fiber. The output power of the generated Stokes light reaches 12.05 W, with a conversion efficiency of 67.4%. Compared to previously reported FWM-based fiber lasers with output power and conversion efficiency below watt level and 50% respectively, our result shows significant improvement. Besides, benefiting from the strict phase match requirement of FWM process, this laser system has unique advantages in suppressing spectral broadening, the output linewidth of which is less than half of the conventional Raman fiber laser under the same power level. Furtherly, we propose a power balance model to describe the power evolution characteristics of the Raman-assisted FWM process, proving the advantage of phosphosilicate fiber in improving the conversion efficiency of FWM process. This work gives a reference for efficient narrow linewidth frequency conversion or amplification.

A five-wavelength-switchable thulium-doped fiber laser with a fiber Bragg grating (FBG)-based five-channel transmitting Fabry-Pérot (F-P) filter and a multi-coupler based triple-ring cavity (CTRC) filter, is experimentally proposed. For the first time, a multi-channel F-P filter and specially-designed coupler-based compound cavity filter were combined to realize multi-wavelength-switchable operation, with single-longitudinal-mode (SLM) lasing for each wavelength channel in a 2 µm band fiber laser. The theoretical analysis of the CTRC filter and the principle for achieving SLM operation by corporately using the F-P filter and CTRC filter were presented in detail. The experimental results demonstrated the good performance of the proposed filters. Five lasing wavelengths (1941.13 nm, 1941.22 nm, 1941.30 nm, 1941.39 nm, and 1941.47 nm) were obtained with good switchability, and each operated in a stable SLM state. The OSNR of each lasing wavelength was higher than 50 dB, and the linewidths of all obtained wavelengths were less than 8 kHz.

The metallic cavity has been recognized as the promising structure to realize the subwavelength nanolasers with the dimensions of mode volumes considerably smaller than the optical diffraction limit. However, the current nanolasers based on metallic cavity are realized in near-infrared ranges, since the high optical loss from metal makes the metallic lasing at the visible wavelength challenging. Here, we propose an innovative approach to fabricate metallic cavity plasmonic nanolaser based on Au-coated perovskite nanowires synthesized by an in situ solution method. The intrinsic ohmic loss of metal could be overcome by the high gain of the perovskite. The laser presents a prominent lasing behavior in the visible range at 548 nm. The mode area is reduced to λ2/48, the Purcell factor reaches up to 108, and the physical dimension is only 150 nm. To be noted, the competition between plasmonic modes and photonic modes was observed for the first time in the metallic cavity nanolasers. This work promotes the application of perovskite composite nanostructures to photonic devices.

We present AlGaAs-based monolithically integrated dual-wavelength lasers and master-oscillator power-amplifiers emitting around 785 nm which combine a near diffraction limited beam quality with single longitudinal mode emission, both achieved over a wide range of output powers. This holds for alternating dual wavelength operation which is of interest for applications in spectroscopy as well as for simultaneous dual wavelength operation which can be used to generate THz-radiation. Compared to previous designs the lateral optical confinement is provided by two differently deep etched ridge waveguides. Shallow etching is used in lasing and amplifying sections to ensure single-lateral mode operation, whereas deep etching is employed to form more compact S-bends and to enable the use of multi-mode interference (MMI) couplers instead of Y-couplers.

This paper comprehensively investigated noise characteristics of superluminal propagation based on low-noise single-frequency Brillouin lasing oscillation with the aid of a population inversion dynamic grating. Thanks to high-degree polarization alignment between the Brillouin pump and the lased Stokes lightwaves in polarization maintaining fibers, efficient Brillouin lasing resonance with over 10-dB relative intensity noise suppression has been demonstrated to activate Brillouin loss-induced anomalous dispersion in the vicinity of pump signals, benefiting a noise-insensitive superluminal propagation along kilometer-long optical fibers with robust resistance to ambient disturbance. Consequently, sinusoidally modulated pump signals experienced the time advancement of 4634.0 ns at the group velocity of 10.63c. Results show that the variance of the fractional advancement with polarization maintaining fibers is 2.54 × 10−4 which is two orders of magnitude lower than that of conventional single mode fibers. Furthermore, the dependence of the group velocity on the modulation frequency was experimentally investigated, showing good agreement with the theoretical analysis.

Auger recombination is known to be a significant non-radiative process limiting near- and mid-infrared quantum well lasers. The one-dimensional confinement of quantum wells and small band offsets (relative to the bandgap) permits two fundamentally different categories of Auger mechanisms to operate. These mechanisms may be identified as either activated or thresholdless in nature. In this work, we investigate the nature of the dominant Auger mechanism in mid-infrared emitting quantum wells by characterizing a range of type-I InGaAsSb quantum well lasers operating within the 2 - 3 μm wavelength range. The temperature dependence of both the threshold current density and integrated spontaneous emission reveal that the threshold current is dominated by radiative recombination up to a break-point temperature (occurring below 200 K). Beyond the break point temperature, the exponential dependence of the threshold current increases rapidly. The deterioration in the stability of lasing threshold indicates that a thermally activated Auger process is dominant in all devices and is sensitive to the population of heavy-holes in the quantum wells.

This work reports on the dynamic evolution of narrow linewidth modes in stochastic Brillouin random fiber lasers with ultra-high resolution time-resolved spectroscopy technique. New fundamental aspects are revealed, including strong mode competition in multimode operation. It shows that single-mode operation is only possible near threshold in pulsed regime. Just above threshold, lasing becomes multimode, still in pulsed regime. Well above threshold quasi-CW multimode operation is observed with strong mode competition, exhibiting high-intensity noise, governed by multimode beating, and slow average intensity variations induced by Rayleigh scattering random fluctuations.

Herein, we demonstrate a highly tunable enhancement and switching of nonlinear emission from all-inorganic metal halide perovskites based on an asymmetrically biased metal-insulator-semiconductor (MIS) structure. We achieve 2 orders of magnitude enhancement of the two-photon-pumped photoluminescence (TPL) from CsPbBr3 microplates with the MIS structure, due to comprehensive effects including localized field effect, trap-filling effect, and collection enhancement. In particular, taking advantage of electric-field-induced passivation/activation of Br vacancies, we realize highly tunable TPL enhancement, ranging from ∼61.2-fold to ∼370.3-fold. Moreover, we demonstrate an efficient modulation of the two-photon-pumped lasing from the MIS structure, which exhibits electric field induced switching with a high on/off ratio of 67:1. This work has opened new avenues for steering carrier transport and nonlinear emission in lead halide perovskites, which shows great promise for realizing high-efficiency and tunable nonlinear nanophotonic devices.

By simulating the dependence of laser directionality and the possibility of multimode lasing on the sidewall angle of Aquarius-shaped cavity, we achieved the optimized parameters for low-coherence and high-directivity laser output. The measured divergence angle, the speckle contrast, and the output power are 7.2°, 4.53 %, 700 mW@4 A, respectively, in the experiment. Then we introduced patterned electrode on the P-side of the laser, and obtained adjustable coherence with the switched speckle contrast between 4.8 % and 27.8 %. This highly directional and adjustable coherence on-chip complex cavity laser prospectively offers a new choice for biological imaging.

Cr3+-doped α-Al2O3 nanoparticles (Al2−xCrxO3, 0.005 ≤ x ≤ 0.05) were synthesized by co-precipitation method. X-ray diffraction (XRD) patterns of Cr3+:Al2O3 nanoparticles revealed the crystallite size of ∼53 nm and electron microscopy (SEM & TEM) confirmed the spherical nanoparticle formation. Diffuse reflectance spectra (DRS) displayed peaks at 406 and 558 nm corresponding to the Cr3+ transitions which became prominent with the increase in Cr3+ concentration which was also evidenced by the gradually increasing pink coloration of the samples. Photoluminescence (PL) studies showed the sharp red emission at 694 nm (ruby line) which was observed for all samples. The Dq/B value for all samples was found to be greater than 2.3 confirming the presence of Cr3+ ions in the octahedral sites. Chromaticity diagrams displayed the maximum red appearance for the sample with x = 0.01 and a lifetime of 4 ms. The synthesized Cr3+:Al2O3 nanoparticles with smaller crystallite sizes and narrow near monochromatic emission can be used in various applications including sensing, lasing, and bioimaging applications.

We experimentally and theoretically demonstrate a new method to obtain a single-mode operation in long cavity lasers. The method is based on suppressing non-lasing modes in the time domain by attenuating their intensity beating with the lasing mode. This suppression is implemented in our experiments by adding into the cavity an intensity modulator, which is controlled by the photo-detected beating signal. We have demonstrated the method in a long Erbium-doped fiber ring laser with a ring cavity length of about 13 m. Single-mode operation without mode-hopping was obtained for a long time duration of about 100 minutes. Although Erbium-doped fiber amplifiers are homogeneously broadened at room temperature, a single-mode operation was achieved in several cavity modes, which do not have the highest small-signal gain. A theoretical model, based on a small-signal stability analysis, is given. The model indicates that the control delay should be accurately chosen.

Summary The remarkable photophysical properties of halide perovskites have led to high-performance lasers. The slow emission dynamics and diffraction-limited device, however, impose an intrinsic barrier on realizing ultrafast and compact lasers for integrated optoelectronic applications. Plasmonic cavities have been employed to reduce laser size. Yet the emission dynamics is fundamentally limited due to the dilemma between ever-reduced cavity size and the increase of losses. Here, we show a subwavelength-scale lasing perovskite with ultrahigh Purcell enhancement of 209 that greatly enhances emission dynamics under ambient conditions. The hybrid surface plasmon polaritons (SPPs) coupled with perovskites significantly reduce plasmonic and trap state loss channels and promote a strong Purcell effect. Moreover, the realization of SPPs confinement away from the perovskite region mitigates gain degradations that enables superior long-term device stability and reliability. Our study opens a new avenue for on-chip ultrafast optoelectronics and fundamental studies of light-matter interactions at the strongly confined field.

We directly compare the performance of 1.55 $\mu \text{m}$ Fabry-Perot lasers using quantum well (QW) and quantum dash gain regions. Other than the gain medium the designs were identical, grown in the same growth system, and processed at the same time. The static laser performance (light-current and spectral) were similar for both gain materials but the intensity and phase noise characteristics of the dash based lasers were significantly better. This was attributed to the self mode-locking of the dash lasers that was not observed for the QW lasers. This reduction in noise allowed individual lasing lines from the Fabry-Perot dash lasers to be used for data transmission using high order modulation schemes, with quadrature phase-shift keying (QPSK) demonstrated at a symbol rate of 32GBaud. This performance could not be achieved using the equivalent QW based laser.

Tunable lasers in the terahertz frequency range are of great demand for many spectroscopic applications. The first continuously tunable p-Ge Landau level terahertz laser had the drawback of pulsed operation at very low temperatures. There have been promising developments of Landau level lasers based on graphene in combination with other two-dimensional materials. Extended theoretical work has resulted in an understanding of carrier dynamics and the relevant Auger and phonon processes. Both optical and electrical pumping schemes have been proposed to achieve inversion and lasing. There are still open questions about the combination of two-dimensional structures and the carrier transfer mechanisms between the layers. By solving the technological challenges, the realization of a near room-temperature Landau level laser can be envisaged. Progress on Landau level lasers—based on external magnetic field splitting of electronic states—is reviewed, with particular attention paid to the potential for tunable terahertz lasers.

Optical vortices with tunable properties in multiple dimensions are highly desirable in modern photonics, particularly for broadly tunable wavelengths and topological charges at the micrometer scale. Compared to solid-state approaches, here we demonstrate tunable optical vortices through the fusion of optofluidics and vortex beams in which the handedness, topological charges, and lasing wavelengths could be fully adjusted and dynamically controlled. Nanogroove structures inscribed in Fabry-Pérot optofluidic microcavities were proposed to generate optical vortices by converting Hermite-Gaussian laser modes. Topological charges could be controlled by tuning the lengths of the nanogroove structures. Vortex laser beams spanning a wide spectral band (430-630 nm) were achieved by alternating different liquid gain materials. Finally, dynamic switching of vortex laser wavelengths in real-time was realized through an optofluidic vortex microlaser device. The findings provide a robust yet flexible approach for generating on-chip vortex sources with multiple dimensions, high tunability, and reconfigurability. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) All the authors would like to thank A*STAR for support. This research is supported by A*STAR under its AME IRG Grant (project no. A20E5c0085). M.K. is also thankful for the support from ACRF Tier 2 (Grant T2EP50120-0003).

Colloidal quantum dots (CQDs) are a promising gain material for solution-processed, wavelength-tunable lasers, with potential application in displays, communications, and biomedical devices. In this work, we combine a CQD film with an array of nanoantennas, made of titanium dioxide cylinders, to achieve lasing via bound states in the continuum (BICs). Here, the BICs are symmetry-protected cavity modes with giant quality factors, arising from slab waveguide modes in the planar CQD film, coupled to the periodic nanoantenna array. We engineer the thickness of the CQD film and size of the nanoantennas to achieve a BIC with good spatial and spectral overlap with the CQDs, based on a second-order transverse-electric (TE)-polarized waveguide mode. We obtain room-temperature lasing with a low threshold of approximately 11 kW/cm2 (peak intensity) under 5-ns-pulsed optical excitation. This work sheds light on the optical modes in solution-processed, distributed-feedback lasers and highlights BICs as effective, versatile, surface-emitting lasing modes.

We report the generation of multiple sets of 3D confined resonant modes in a single microtube cavity owing to nanogap induced resonant trajectory splits. The optical field largely overlaps in the split resonant trajectories, enabling strong optical coupling of 3D confined resonant light. The anticrossing feature and modes changing-over were demonstrated as direct evidence of strong coupling. In such an optical coupling system, the spatial optical field distribution of 3D coupling modes was experimentally mapped under the strong coupling regime, which allows direct observation of the energy transfer process between two hybrid states. Numerical calculations based on a quasi-potential model and the mode detuning process are in excellent agreement with the experimental results. The generation of multiple sets of 3D confined resonant modes and their efficient coupling in a single microcavity are of high interest for directional coupling with a higher degree of freedom to realize on-chip integration with elevated functionalities such as multiplexing, 3D lasing, and signal processing.

Bianisotropy is a powerful concept enabling asymmetric optical response, including asymmetric reflection, absorption, optical forces, light trapping, and lasing. The physical origin of these asymme...

Optically pumped wavelength-tunable vertical-cavity surface-emitting lasers (VCSELs) operating in the ultraviolet A (UVA) spectrum were demonstrated. The VCSELs feature double dielectric distributed brag reflectors and a wedge-shaped cavity fabricated using the substrate transfer technique and laser lift off, resulting in a graded cavity length in one device. A resonant period gain structure is used in the InGaN/GaN multi-quantum well active region to enhance the coupling between the cavity mode field and the active layers. The optical field inside the cavity is modulated by the cavity length; thus, tunable lasing at different wavelengths is realized at different points of a single VCSEL chip. The lasing wavelength extends from 376 to 409 nm, covering most of the UVA band below the band gap of GaN. The threshold pumping power density of the UVA VCSELs at different wavelengths ranges from 383 to 466 kW/cm2, which is among the lowest values for ultraviolet (UV) VCSELs. This study is promising for the development of small-footprint, power-efficient UV light sources.

We investigate numerically the chaotic dynamics of optically pumped quantum-dot (QD) spin vertically coupled surface emitting lasers (VCSELs) accounting for both ground state (GS) and excited state (ES) energy levels through the elaboration of the spin-flip model (SFM). The intensity dynamics associated with ES and GS transitions are studied by means of the largest Lyapunov exponent (LLE) and stability maps in terms of operational parameters (pump ellipticity and pump intensity), as well as material parameters (ES–GS intraband relaxation rate, spin relaxation rate and birefringence), are produced. It is established that although both ES and GS dynamics exhibit the same kind of nonlinear dynamics for a given set of control parameters, the ES and GS dynamics are weakly uncorrelated. This can be the basis for the realization of various functionalities including reservoir computing.

A tunable dual-wavelength Brillouin-bismuth fiber laser with a triple-Brillouin frequency spacing of ∼37.8 GHz was demonstrated by employing modular structures. The modular designs can be divided into two main cavities, whereby cavity 1 consisted of a 2-km single-mode fiber (SMF) and a loop mirror that was able to generate a single-spaced Brillouin shift, while cavity 2 comprised of 10-km dispersion compensating fiber (DCF) that was able to produce a double-spaced Brillouin shift. Based on this design, a stable dual-wavelength lasing was established with a low peak power fluctuation of 0.13 dB and 0.6 dB for the Brillouin pump (BP) and third Brillouin Stokes line (BS3), respectively. By varying the center wavelength of the Brillouin pump, the dual-wavelength laser can be tuned across a 40 nm span, ranging from 1300 nm to 1340 nm. The frequency spacing of the Brillouin-bismuth fiber laser can also be easily switched between ∼12.6 GHz, ∼25.2 GHz, and ∼37.8 GHz by utilizing these modular structures. The proposed dual-wavelength laser has a promising potential for application as a low phase noise source for microwave generation.

Among perovskite semiconductors, quasi-two-dimensional (2D) materials are attractive for the pursuit of electrically driven lasing given their excellent performance in light-emitting diodes (LEDs) and their recent success in continuous-wave optically pumped lasing. We investigate the spontaneous photoluminescence emission and amplified spontaneous emission (ASE) of a series of quasi-2D emitters, and their directly analogous 3D materials formed by removing the 2D organic spacer by annealing. Although the PL photoluminescence (PL) (at low optical excitation power) from quasi-2D films with high 2D spacer fractions can be much brighter than that from their 3D counterparts, the ASE thresholds of these quasi-2D materials tend to be higher. This counter-intuitive behavior is investigated through time-resolved photophysical studies, which reveal the emission in the high-spacer-content quasi-2D perovskite can be exclusively excitonic, and the exciton–exciton annihilation of quasi-2D perovskite starts to take over the exciton dynamics at a low exciton density (

Although laser-induced graphene (LIG) has great advantages in the cost and manufacturing process, it has been seldom reported in the field of electromagnetic interference (EMI) shielding due to its unobtrusive conductivity and the limitation of inherent substrates. In this work, polybenzoxazine is chosen as precursor to fabricate the LIG via a one-step defocused lasing process. As a result of favorable porous structures and high conductivity, the as-produced LIG exhibits the EMI shielding effectiveness up to 24.8 dB in X-band at the thickness of 68 μm. And the EMI shielding effectiveness of LIG/Fe3O4 composite is increased to 32.7 dB at a smaller thickness of 53 μm which is obtained by a solvent-free approach. When considering the thickness and lightweight properties, the absolute shielding effectiveness is also surpassing most of the other carbon-based shielding materials. More importantly, taking advantage of the difference in the thermal expansion coefficient of carbon material and polymeric substrate, we develop a rapid quench-peeling (RQP) strategy for the separation of LIG from polymeric substrate to obtain the free-standing LIG film. Moreover, the structures and properties of LIG are well preserved. The free-standing LIG films after peeling have wider adaptability in practical EMI shielding applications, and also opened up possibilities for use in other fields, such as Joule heating device.

We perform a detailed comparison of 2D Auger coefficients in narrow-gap type-I and type-II quantum wells (T1QWs and T2QWs), and the relative effects of Auger non-radiative decay on midwave infrared lasers employing both types of gain media. Comparison is also made to 3D Auger coefficients in bulk mid-IR materials, by defining a “normalization length” that accounts for the spatial extent of the electron and hole wavefunctions in the quantum wells. The comparisons confirm that Auger recombination in both types of QW is substantially suppressed relative to bulk, due primarily to the effects of compressive strain on the valence subband dispersions. We find that the 2D Auger coefficients in T1QWs remain substantially lower than those in T2QWs out to wavelengths beyond $3.5~\mu \text{m}$ . However, this does not necessarily imply a lower lasing threshold because a substantial fraction of the holes injected into T1QWs occupy lower subbands that do not contribute gain, so more must be injected to reach the lasing threshold. When all of the relevant considerations are combined, the thresholds for the best T1QW and T2QW lasers cross over near $\lambda ~\approx ~3.0~\mu \text{m}$ . Other characteristics governing the relative T1QW and T2QW laser performances above threshold, such as maximum output power and wallplug efficiency, are also considered.

Drop-based microcavity lasers emerged as a promising tool in modern physics investigation and chemical detection owing to their cost-effective fabrication, high luminescence, and sensitive molecule sensing. However, it is of great challenge to achieve highly directional emission along with high quality (Q) factors via traditional droplet self-assembly behavior of the gain medium on a planar substrate. In this work, a single-mode microcavity laser with directional far-field emission is first proposed via droplet self-assembly 3D-curved microcavities, and simultaneously, acetic acid (AcOH) gas sensing is realized. Trichromatic single-mode lasing in 3D-curved microcavities with distinct organic polymer droplets is constructed on silica fibers via a self-assembly procedure. By regulating the curvature of the substrate, mode selection and directional emission of the lasing action are realized. The measured Q-factor of the proposed anisotropic 3D-curved active microcavity is ∼20k. Furthermore, on account of the sensitive responsiveness of liquid organic polymers, single-mode laser sensors can be realized by measuring the shift of their lasing modes on exposure to organic vapor. Benefiting from chemical reaction with rhodamine 6G, the AcOH gas sensor displays a short response time. These results may open new insights into drop-based quasi-3D-anisotropic whispering-gallery-mode microcavities to improve the development of lab-in-a-droplet, ranging from a tuneable microcavity laser to a chemical gas sensor.

A distributed temperature monitoring inside a cavity of ytterbium DFB and holmium fiber lasers has been demonstrated with a spatial resolution of 1 and 5 mm, respectively, for the first time to the best of our knowledge. For this, we use an optical backscatter reflectometer, which measures intracore temperature, and compare it with the data of an IR thermographic camera, which measures temperature from the surface of a fiber. In the case of holmium fiber laser pumped at a wavelength of 1125 nm with a power of 6 W, the maximum temperature variation along the ∼3-m active fiber reaches ∼60 °C. In the case of ytterbium DFB laser, we observe a strong inhomogeneity of the temperature along the DFB cavity, which leads to a significant decrease in the lasing efficiency. When pumped by a single-mode laser diode at a wavelength of 976 nm with a power of up to 526 mW, the maximum temperature difference reaches 37 °C for the 37-mm DBF cavity.

Resistive strain and bending sensors offer a versatile platform for sensing various physical parameters with relatively little effort and budget. The lightweight, robust and compact sensors are extensively used in manifold low-power applications. Recently, scribed and flexible laser-induced graphene sensors have shown potent capabilities for a variety of measurements, including flow, deflection, and force. Achieving a high sensitivity to various stimuli remains a challenge due to limited change in relative resistance. In this paper, we report a multifunctional LIG sensor with widely tunable properties and significantly enhanced electromechanical performance. A method of repeated laser writing is used to increase the porosity, the uniform carbonization degree and, most importantly, the sensitivity of the LIG sensors. A gauge factor of 91.2 is achieved after three-times laser writing at low power, which is an increase of 750% to one-time laser writing and 720% higher than the ones previously reported for LIG strain sensors. The increase is attributed to a more porous surface morphology that provides more overlapping area and displacement of the graphene layers. A homogeneous bidirectional response was obtained by scribing the electrodes on both faces of the substrate. Parylene C-coating is used to protect the LIG sensors from environmental effects. Coated sensors were packaged to a PCB assembly for easy integration into various applications. An example is a LIG bending sensor customized for velocity profile monitoring of Unmanned Aerial Vehicles in the outdoor environment.

Plasmon mode engineering enables the ability to manipulate the highly localized electromagnetic fields at the deep-subwavelength scale. Here, without introducing geometrical asymmetry, we propose a scheme to generate and control the asymmetric plasmon mode in a single nanowire cavity by the interference of cavity modes with opposite parities. Through a rigorous theoretical derivation and further verification with finite-element analysis, we show that the simultaneous excitation of odd and even cavity modes with mutual spectral and spatial overlap in a single nanowire enables a new hybridized plasmon mode with strong near-field directionality and high extinction ratio. By full exploitation of the incident electromagnetic field including its amplitude, phase, and spin components, the behavior of the asymmetric plasmon mode with its asymmetric field can be readily controlled over a broad wavelength range, offering versatility for controlling the cavity plasmon's spatial and spectral distribution at the nanoscale. Our approach can be applied to modulate the light-matter interaction and other functional devices in applications such as cavity quantum electrodynamics, information processing, sensing and lasing.

Single-mode plasmonic lasing has great potential for use in photonic and sensing applications. In this work, single-mode lasing is realized using a plasmonic-enhanced woven microfiber that shows ultrahigh sensitivity to the ambient environment. This plasmonic-enhanced microfiber is fabricated by spraying Ag nanospheres onto rhodamine 6G-doped polymer microfibers. Single-mode laser emission with an ultranarrow linewidth (0.1 nm) and a low threshold (18.8 kW/mm2) is achieved in the microfiber using the effects of mode selection and plasmonic enhancement provided by the Ag nanospheres. A large wavelength shift in the single-mode lasing is observed when the proposed laser is used as a sensor and exposed to a humid or acidic environment. The wavelength shift is attributed to refractive index variations in the microfiber caused by either moisture absorption or chemical reactions. In humidity sensing, the laser's sensitivity is as high as 826.6 pm/% relative humidity (RH) and the detection limit is 0.051% RH. An innovative strategy for acetic acid gas sensing is proposed that uses the chemical reaction with rhodamine 6G, and its minimum response time is 5 min. Because of the microfiber's excellent fabric compatibility, a wearable sensor is fabricated by weaving the plasmonic-enhanced microfiber into clothes, and this sensor demonstrates extreme bending stability. The results reported here provide a novel approach to the design and fabrication of ultrasensitive wearable sensors for multifunctional sensing applications.