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Vol. 4 ， Issue 3 ， 2015
- Abstract：Nucleic acid amplification and quantification via polymerase chain reaction (PCR) is one of the most sensitive and powerful tools for clinical laboratories, precision medicine, personalized medicine, agricultural science, forensic science and environmental science. Ultrafast multiplex PCR, characterized by low power consumption, compact size and simple operation, is ideal for timely diagnosis at the point-of-care (POC). Although several fast/ultrafast PCR methods have been proposed, the use of a simple and robust PCR thermal cycler remains challenging for POC testing. Here, we present an ultrafast photonic PCR method using plasmonic photothermal light-to-heat conversion via photon–electron–phonon coupling. We demonstrate an efficient photonic heat converter using a thin gold (Au) film due to its plasmon-assisted high optical absorption (approximately 65% at 450 nm, the peak wavelength of heat source light-emitting diodes (LEDs)). The plasmon-excited Au film is capable of rapidly heating the surrounding solution to over 150 ℃ within 3 min. Using this method, ultrafast thermal cycling (30 cycles; heating and cooling rate of 12.79±0.93 ℃ s−1 and 6.6±0.29 ℃ s−1, respectively) from 55 ℃ (temperature of annealing) to 95 ℃ (temperature of denaturation) is accomplished within 5 min. Using photonic PCR thermal cycles, we demonstrate here successful nucleic acid (λ-DNA) amplification. Our simple, robust and low cost approach to ultrafast PCR using an efficient photonic-based heating procedure could be generally integrated into a variety of devices or procedures, including on-chip thermal lysis and heating for isothermal amplifications.Keywords：genomics;light-emitting diodes (LEDs);molecular diagnostics;personalized medicine;plasmonics;point-of-care (POC) diagnostics;polymerase chain reaction (PCR)
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Published：2024-09-25 - Abstract：Precise information about the temporal mode of optical states is crucial for optimizing their interaction efficiency between themselves and/or with matter in various quantum communication devices. Here we propose and experimentally demonstrate a method of determining both the real and imaginary components of a single photon's temporal density matrix by measuring the autocorrelation function of the photocurrent from a balanced homodyne detector at multiple local oscillator frequencies. We test our method on single photons heralded from biphotons generated via four-wave mixing in an atomic vapor and obtain excellent agreement with theoretical predictions for several settings.Keywords：autocorrelation matrix;polychromatic optical heterodyne tomography;single photon;temporal mode function
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Published：2024-09-25 - Abstract：Cascaded optical field enhancement (CFE) can be realized in some specially designed multiscale plasmonic nanostructures, in which the generation of extremely strong fields at nanoscale volume is crucial for many applications, for example, surface-enhanced Raman spectroscopy (SERS). In this paper, we propose a strategy for realizing a high-quality plasmonic nanoparticle-in-cavity (PIC) nanoantenna array, in which strong coupling between a nanoparticle (NP) dark mode with a high-order nanocavity bright mode can produce strong Fano resonance at the target wavelength. The Fano resonance can effectively boost the CFE in a PIC. A cost-effective and reliable nanofabrication method is developed using room temperature nanoimprinting lithography to manufacture high-quality PIC arrays. This technique guarantees the generation of only one gold NP at the bottom of each nanocavity, which is crucial for the generation of the expected CFE. To demonstrate the performance and application of the PIC array, the PIC array is employed as an active SERS substrate for detecting 4-aminothiophenol molecules. An experimental SERS enhancement factor of 2 × 107 is obtained, which verifies the field enhancement and the potential of this device.Keywords：cascaded optical field enhancement;Fano resonance;localized surface plasmon;plasmonic nanoantenna;surface-enhanced Raman spectroscopy
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Published：2024-09-25 - Abstract：Optical spectral measurements are crucial for optical sensors and many other applications, but the prevailing methods, such as optical spectrum analysis and tunable laser spectroscopy, often have to make compromises among resolution, speed, and accuracy. Optical frequency combs are widely used for metrology of discrete atomic and molecular spectral lines. However, they are usually generated by optical methods and have large comb spacing, which limits the resolution for direct sampling of continuous spectra. To overcome these problems, this paper presents an original method to digitally generate an ultrafine optical frequency comb (UFOFC) as the frequency ruler for spectral measurements. Each comb line provides one sampling point, and the full spectrum can be captured at the same time using coherent detection. For an experimental demonstration, we adopted the inverse fast Fourier transform to generate a UFOFC with a comb spacing of 1.46 MHz over a 10-GHz range and demonstrated its functions using a Mach-Zehnder refractive index sensor. The UFOFC obtains a spectral resolution of 0.01 pm and response time of 0.7 μs; both represent 100-fold improvements over the state of the art and could be further enhanced by several orders of magnitude. The UFOFC presented here could facilitate new label-free sensor applications that require both high resolution and fast speed, such as measuring binding kinetics and single-molecule dynamics.Keywords：coherent detection;digital signal process;optical frequency combs;optical sensors;optical spectrometry
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Published：2024-09-25 - Abstract：Here, we introduce the first experimental proof of coherent oscillation and coupling of photoswitchable molecules embedded randomly in a polymeric matrix and acting cooperatively upon illumination with UV light. In particular, we demonstrate the specular reflection and Brewster phenomenon alteration of photochromic molecular dipole antennas. We successfully demonstrate the concept of Brewster wavelength, which is based on the dipolar interaction between radiating dipoles and the surrounding matrix possessing a net dipole moment, as a key tool for highly localized sensing of matrix polarity. We also introduce the concept of 'tailored molecular photonic coupling' while highlighting the role of interferences for the design of optically active media by adjusting the photonic response of the medium with the real and imaginary refractive index of photoswitchable molecules in the 'ON' state. Our results enhance our fundamental understanding of coherent dipole radiation and open a new vein of research based on glassy disordered dipolar composites that act as macroscopic antenna with cooperative action; furthermore, these results have important implications for new design rules of tailored photonics.Keywords：Brewster angle;coherent coupling;collective oscillation;photoswitchable molecular photonics;specular reflection
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Published：2024-09-25 - Abstract：The predicted extraordinary properties of carbon nanotubes (CNTs) from theoretical calculations have great potential for many applications. However, reliable experimental determination of intrinsic properties at the single-tube level is currently a matter of concern, and many challenges remain because of the unhandled and nanoscale size of individual nanotubes. Here, we demonstrated a prototype to detect the intrinsic thermal conductivity of the single-wall carbon nanotube (SWCNT) and verify the significant non-resonant optical absorption behavior on tiny nanotubes by integrating the nanotube and ice into a new core-shell design. In particular, a reversible optical visualization method based on the individual suspended ultra-long SWCNT was first developed by wrapping a nanotube with ice in the cryogenic air environment. The light-induced thermal effect on the hybrid core-shell structure was used to melt the ice shell, which subsequently acted as a temperature sensor to verify the intrinsic thermal conductivity of the core-like nanotube. More interestingly, we successfully determined for the first time the thermal response phenomenon of the tiny absorption cross section in SWCNT in the vertical-polarization configuration and the significant non-resonant absorption behavior in the parallel-polarization configuration. These investigations will provide a better understanding for the unique optical behaviors of CNT and enable the detection of intrinsic properties of various one-dimensional nanostructures such as nanotubes, nanowires, and nanoribbons.Keywords：carbon nanotube;optical visualization;polarized laser;resonant absorption
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Published：2024-09-25 - Abstract：The process of high harmonic generation (HHG) enables the development of table-top sources of coherent extreme ultraviolet (XUV) light. Although these are now matured sources, they still mostly rely on bulk laser technology that limits the attainable repetition rate to the low kilohertz regime. Moreover, many of the emerging applications of such light sources (e.g., photoelectron spectroscopy and microscopy, coherent diffractive imaging, or frequency metrology in the XUV spectral region) require an increase in the repetition rate. Ideally, these sources are operated with a multi-MHz repetition rate and deliver a high photon flux simultaneously. So far, this regime has been solely addressed using passive enhancement cavities together with low energy and high repetition rate lasers. Here, a novel route with significantly reduced complexity (omitting the requirement of an external actively stabilized resonator) is demonstrated that achieves the previously mentioned demanding parameters. A krypton-filled Kagome photonic crystal fiber is used for efficient nonlinear compression of 9 µJ, 250 fs pulses leading to ~7 µJ, 31 fs pulses at 10.7 MHz repetition rate. The compressed pulses are used for HHG in a gas jet. Particular attention is devoted to achieving phase-matched (transiently) generation yielding >1013 photons s−1 (>50 µW) at 27.7 eV. This new spatially coherent XUV source improved the photon flux by four orders of magnitude for direct multi-MHZ experiments, thus demonstrating the considerable potential of this source.Keywords：coherent extreme ultraviolet sources;high average power;high harmonic generation;nonlinear compression;ultrafast laser
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Published：2024-09-25 - Abstract：We present a new approach for predicting spatial phase signals originating from photothermally excited metallic nanoparticles of arbitrary shapes and sizes. The heat emitted from such a nanoparticle affects the measured optical phase signal via changes in both the refractive index and thickness of the nanoparticle surroundings. Because these particles can be bio-functionalized to bind certain biological cell components, they can be used for biomedical imaging with molecular specificity, as new nanoscopy labels, and for photothermal therapy. Predicting the ideal nanoparticle parameters requires a model that computes the thermal and phase distributions around the particle, thereby enabling more efficient phase imaging of plasmonic nanoparticles and avoiding trial-and-error experiments while using unsuitable nanoparticles. The proposed nonlinear model is the first to enable the prediction of phase signatures from nanoparticles with arbitrary parameters. The model is based on a finite-volume method for geometry discretization and an implicit backward Euler method for solving the transient inhomogeneous heat equation, followed by calculation of the accumulative phase signal. To validate the model, we compared its results with experimental results obtained for gold nanorods of various concentrations, which we acquired using a custom-built wide-field interferometric phase microscopy system.Keywords：digital holographic microscopy;interferometric imaging;nanoparticles;phase measurement;plasmonics
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Published：2024-09-25 - Abstract：The terahertz region is a special region of the electromagnetic spectrum that incorporates the advantages of both microwaves and infrared light waves. In the past decade, metamaterials with effective medium parameters or gradient phases have been studied to control terahertz waves and realize functional devices. Here, we present a new approach to manipulate terahertz waves by using coding metasurfaces that are composed of digital coding elements. We propose a general coding unit based on a Minkowski closed-loop particle that is capable of generating 1-bit coding (with two phase states of 0 and 180°), 2-bit coding (with four phase states of 0, 90°, 180°, and 270°), and multi-bit coding elements in the terahertz frequencies by using different geometric scales. We show that multi-bit coding metasurfaces have strong abilities to control terahertz waves by designing-specific coding sequences. As an application, we demonstrate a new scattering strategy of terahertz waves—broadband and wide-angle diffusion—using a 2-bit coding metasurface with a special coding design and verify it by both numerical simulations and experiments. The presented method opens a new route to reducing the scattering of terahertz waves.Keywords：coding;diffusion;metasurface;terahertz waves
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Published：2024-09-25 - Abstract：A slow-light effect based on metamaterial-induced transparency (MIT) possesses great practical applications for integrated photonic devices. However, to date, only very weak slow-light effects have been obtained in metamaterials because of the intrinsic loss of metal. Moreover, no active control of slow-light has been achieved in metamaterials. Here, we report the realization of a giant slow-light effect on an ultrathin metasurface that consists of periodic arrays of gold nanoprism dimers with a thickness of 40 nm sandwiched between a multilayer-graphene micro-sheet/zinc oxide nanoparticle layer and a monolayer graphene/polycrystalline indium tin oxide layer. The strong field confinement of the plasmonic modes associated with the MIT ensures a tremendous reduction in the group velocity around the transparency window. A group index of more than 4 × 103 is achieved, which is one order of magnitude greater than that of previous reports. A large tunable wavelength range of 120 nm is achieved around the center of the transparency window when the pump light intensity is only 1.5 kW cm−2. The response time is as fast as 42.3 ps. These results demonstrate the potential for the realization of various functional integrated photonic devices based on metasurfaces, such as all-optical buffers and all-optical switches.Keywords：graphene;metamaterial-induced transparency;metasurfaces;slow light effect;Zno nanoparticles
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Published：2024-09-25 - Abstract：Light trapping within waveguides is a key practice of modern optics, both scientifically and technologically. Photonic crystal fibers traditionally rely on total internal reflection (index-guiding fibers) or a photonic bandgap (photonic-bandgap fibers) to achieve field confinement. Here, we report the discovery of a new light trapping within fibers by the so-called Dirac point of photonic band structures. Our analysis reveals that the Dirac point can establish suppression of radiation losses and consequently a novel guided mode for propagation in photonic crystal fibers. What is known as the Dirac point is a conical singularity of a photonic band structure where wave motion obeys the famous Dirac equation. We find the unexpected phenomenon of wave localization at this point beyond photonic bandgaps. This guiding relies on the Dirac point rather than total internal reflection or photonic bandgaps, thus providing a sort of advancement in conceptual understanding over the traditional fiber guiding. The result presented here demonstrates the discovery of a new type of photonic crystal fibers, with unique characteristics that could lead to new applications in fiber sensors and lasers. The Dirac equation is a special symbol of relativistic quantum mechanics. Because of the similarity between band structures of a solid and a photonic crystal, the discovery of the Dirac-point-induced wave trapping in photonic crystals could provide novel insights into many relativistic quantum effects of the transport phenomena of photons, phonons, and electrons.Keywords：band structure;Dirac equation;optical fiber;optical mode;photonic crystal
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Published：2024-09-25 - Abstract：Metasurfaces offer unprecedented flexibility in the design and control of light propagation, replacing bulk optical components and exhibiting exotic optical effects. One of the basic properties of the metasurfaces, which renders them as frequency selective surfaces, is the ability to transmit or reflect radiation within a narrow frequency band that can be engineered on demand. Here we introduce and demonstrate experimentally in the THz domain the concept of wavevector selective surfaces – metasurfaces transparent only within a narrow range of light propagation directions operating effectively as tunnel vision filters. Practical implementations of the new concept include applications in wavefront manipulation, observational instruments, vision and free-space communication in light-scattering environments.Keywords：flat optics;metafilms;metasurfaces;planar metamaterials;wavefront manipulation
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Published：2024-09-25 - Abstract：The application of three-dimensional (3D) plasmonic nanostructures as metamaterials (MMs), nano-antennas, and other devices faces challenges in producing metallic nanostructures with easily definable orientations, sophisticated shapes, and smooth surfaces that are operational in the optical regime and beyond. Here, we demonstrate that complex 3D nanostructures can be readily achieved with focused-ion-beam irradiation-induced folding and examine the optical characteristics of plasmonic "nanograter" structures that are composed of free-standing Au films. These 3D nanostructures exhibit interesting 3D hybridization in current flows and exhibit unusual and well-scalable Fano resonances at wavelengths ranging from 1.6 to 6.4 µm. Upon the introduction of liquids of various refractive indices to the structures, a strong dependence of the Fano resonance is observed, with spectral sensitivities of 1400 nm and 2040 nm per refractive index unit under figures of merit of 35.0 and 12.5, respectively, for low-order and high-order resonance in the near-infrared region. This work indicates the exciting, increasing relevance of similarly constructed 3D free-standing nanostructures in the research and development of photonics and MMs.Keywords：extraordinary Fano resonances;plasmonic nanostructures;spatially oriented;substrate-free;three-dimensional
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Published：2024-09-25 - Abstract：Photonic and plasmonic devices rely on nanoscale control of the local density of optical states (LDOS) in dielectric and metallic environments. The tremendous progress in designing and tailoring the electric LDOS of nano-resonators requires an investigation tool that is able to access the detailed features of the optical localized resonant modes with deep-subwavelength spatial resolution. This scenario has motivated the development of different nanoscale imaging techniques. Here, we prove that a technique involving the combination of scanning near-field optical microscopy with resonant scattering spectroscopy enables imaging the electric LDOS in nano-resonators with outstanding spatial resolution (λ/19) by means of a pure optical method based on light scattering. Using this technique, we investigate the properties of photonic crystal nanocavities, demonstrating that the resonant modes appear as characteristic Fano line shapes, which arise from interference. Therefore, by monitoring the spatial variation of the Fano line shape, we locally measure the phase modulation of the resonant modes without the need of external heterodyne detection. This novel, deep-subwavelength imaging method allows us to access both the intensity and the phase modulation of localized electric fields. Finally, this technique could be implemented on any type of platform, being particularly appealing for those based on non-optically active material, such as silicon, glass, polymers, or metals.Keywords：nanocavity;nanophotonics;near-field;phase retrieval;resonant-scattering
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Published：2024-09-25 - Abstract：Light emitting diode (LED) lighting is becoming more and more popular, as incandescent lamps are being phased out globally. LEDs have several advantages over incandescent lamps, including energy efficiency, robustness, long lifetime, and good temporal stability. The three latter features make LEDs attractive candidates as new photometric standards. Because the spectra of white LEDs are limited to the visible wavelength range, a novel method for the realization of photometric units based on the predictable quantum efficient detector (PQED) can be utilized. The method eliminates the need of photometric filters that are traditionally used in photometry, and instead relies on carrying out the photometric weighting numerically based on the measured relative spectrum of the source. The PQED-based realization simplifies the traceability chain of photometric measurements significantly as compared with the traditional filter-based method. The measured illuminance values of a white LED deviate by only 0.03% when determined by the new and the traditional methods. The new PQED method has significantly lower expanded uncertainty of 0.26% (k = 2) as compared with that of the traditional filter-based method of 0.42% (k = 2). Furthermore, when filtered photometers that measure LED lighting are calibrated using LED lamps as calibration sources instead of incandescent lamps, a significant decrease in the uncertainty related to the spectral mismatch correction can be obtained. The maximum spectral mismatch errors of LED measurements decreased on average by a factor of 3 when switching from an incandescent lamp to an LED calibration source.Keywords：LED;optical metrology;photometry;standard lamp
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Published：2024-09-25 - Abstract：Monolayer phosphorene provides a unique two-dimensional (2D) platform to investigate the fundamental dynamics of excitons and trions (charged excitons) in reduced dimensions. However, owing to its high instability, unambiguous identification of monolayer phosphorene has been elusive. Consequently, many important fundamental properties, such as exciton dynamics, remain underexplored. We report a rapid, noninvasive, and highly accurate approach based on optical interferometry to determine the layer number of phosphorene, and confirm the results with reliable photoluminescence measurements. Furthermore, we successfully probed the dynamics of excitons and trions in monolayer phosphorene by controlling the photo-carrier injection in a relatively low excitation power range. Based on our measured optical gap and the previously measured electronic energy gap, we determined the exciton binding energy to be ~0.3 eV for the monolayer phosphorene on SiO2/Si substrate, which agrees well with theoretical predictions. A huge trion binding energy of ~100 meV was first observed in monolayer phosphorene, which is around five times higher than that in transition metal dichalcogenide (TMD) monolayer semiconductor, such as MoS2. The carrier lifetime of exciton emission in monolayer phosphorene was measured to be ~220 ps, which is comparable to those in other 2D TMD semiconductors. Our results open new avenues for exploring fundamental phenomena and novel optoelectronic applications using monolayer phosphorene.Keywords：exciton;monolayer phosphorene;optical injection;two-dimensional materials
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Published：2024-09-25 - Abstract：The multicore fiber (MCF) is a physical system of high practical importance. In addition to standard exploitation, MCFs may support discrete vortices that carry orbital angular momentum suitable for spatial-division multiplexing in high-capacity fiber-optic communication systems. These discrete vortices may also be attractive for high-power laser applications. We present the conditions of existence, stability, and coherent propagation of such optical vortices for two practical MCF designs. Through optimization, we found stable discrete vortices that were capable of transferring high coherent power through the MCF.Keywords：coherent energy propagation;multicore fibers;nonlinear vortices
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Published：2024-09-25
Original Articles
- Abstract：The properties of propagating surface plasmon polaritons (SPPs) along one-dimensional metal structures have been investigated for more than 10 years and are now well understood. Because of the high confinement of electromagnetic energy, propagating SPPs have been considered to represent one of the best potential ways to construct next-generation circuits that use light to overcome the speed limit of electronics. Many basic plasmonic components have already been developed. In this review, researches on plasmonic waveguides are reviewed from the perspective of plasmonic circuits. Several circuit components are constructed to demonstrate the basic function of an optical digital circuit. In the end of this review, a prototype for an SPP-based nanochip is proposed, and the problems associated with building such plasmonic circuits are discussed. A plasmonic chip that can be practically applied is expected to become available in the near future.Keywords：nanophotonics;plasmonic chip;plasmonic circuit;surface plasmons;waveguide
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Published：2024-09-25 - Abstract：The performance of ultrafast semiconductor disk lasers has rapidly advanced in recent decades. The strong interest from industry for inexpensive, compact, and reliable ultrafast laser sources in the picosecond and femtosecond domains has driven this technology toward commercial products. Frequency metrology and biomedical applications would benefit from sub-200-femtosecond pulse durations with peak powers in the kilowatt range. The aim of this review is to briefly describe the market potential and give an overview of the current status of mode-locked semiconductor disk lasers. Particular focus is placed on the ongoing efforts to achieve shorter pulses with higher peak powers.Keywords：lasers;modelocked lasers;semiconductor lasers;ultrafast lasers;vertical emitting lasers
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Published：2024-09-25
Reviews
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