Broadband bidirectional Brillouin–Raman random fiber laser with ultra-narrow linewidth

We present a Brillouin–Raman random fiber laser(BRRFL)with full-open linear cavity structure to generate broadband Brillouin frequency comb(BFC)with double Brillouin-frequency-shift spacing.The incorporation of a regeneration portion consisting of an erbium-doped fiber and a single-mode fiber enables the generation of broadband BFC.The dynamics of broadband BFC generation changing with the pump power(EDF and Raman)and Brillouin pump(BP)wavelength are investigated in detail,respectively.Under suitable conditions,the bidirectional BRRFL proposed can produce a flatamplitude BFC with 40.7-nm bandwidth ranging from 1531 nm to 1571.7 nm,and built-in 242-order Brillouin Stokes lines(BSLs)with double Brillouin-frequency-shift spacing.Moreover,the linewidth of single BSL is experimentally measured to be about 2.5 kHz.The broadband bidirectional narrow-linewidth BRRFL has great potential applications in optical communication,optical sensing,spectral measurement,and so on.

Wavelength-interval switchable Brillouin–Raman random fiber laser through Brillouin pump manipulation

A wavelength-interval switchable Brillouin–Raman random fiber laser(BRRFL) based on Brillouin pump(BP) manipulation is proposed in this paper. The proposed wavelength-interval switchable BRRFL has a full-open cavity configuration, featuring multiwavelength output with wavelength interval of double Brillouin frequency shifts. Through simultaneously injecting the BP light and its first-order stimulated Brillouin-scattered light into the cavity, the laser output exhibits a wavelength interval of single Brillouin frequency shift. The wavelength-interval switching effect can be manipulated by controlling the power of the first-order stimulated Brillouin scattering light. The experimental results show the multiwavelength output can be switched between double Brillouin frequency shift multiwavelength emission with a broad bandwidth of approximately 60 nm and single Brillouin frequency shift multiwavelength emission of 44 nm. The flexible optically controlled random fiber laser with switchable wavelength interval makes it useful for a wide range of applications and holds significant potential in the field of wavelength-division multiplexing optical communication.

Wavelength switchable mode-locked fiber laser with a few-mode fiber filter

We have proposed and constructed a few-mode fiber(FMF)-based comb filter realized by dislocation splicing a fewmode long-period fiber grating(FM-LPFG) with a single-mode fiber(SMF). From an all-fiber laser with a FMF-based comb filter, the generation of switchable single-, dual-, triple-, and quadruple-wavelength continuous light has been achieved.Moreover, wavelength switchable mode-locked pulses have been obtained with the increased pump power. In the experiment, the output wavelength of the mode-locked fiber laser was changed from 1567.72 nm to 1571.04 nm, while the signal-to-noise(SNR) ratio was maintained above 61 d B. The switchable multiwavelength continuous wave(CW) and mode-locked all-fiber lasers have potentially important applications for fiber sensing, wavelength-division multiplexing(WDM) and signal processing.

A two-step quantum secure direct communication protocol with hyperentanglement

We propose a two-step quantum secure direct communication （QSDC） protocol with hyperentanglement in both the spatial-mode and the polarization degrees of freedom of photon pairs which can in principle be produced with a beta barium borate crystal. The secret message can be encoded on the photon pairs with unitary operations in these two degrees of freedom independently. This QSDC protocol has a higher capacity than the original two-step QSDC protocol as each photon pair can carry 4 bits of information. Compared with the QSDC protocol based on hyperdense coding, this QSDC protocol has the immunity to Trojan horse attack strategies with the process for determining the number of the photons in each quantum signal as it is a one-way quantum communication protocol.

Spatiotemporal mode-locked multimode fiber laser with dissipative four-wave mixing effect

The high degree of freedom and novel nonlinear phenomena of multimode fiber are attracting attention. In this work,we demonstrate a spatiotemporal mode-locked multimode fiber laser, which relies on microfiber knot resonance(MKR) via dissipative four-wave-mixing(DFMW) to achieve high-repetition-rate pulses. Apart from that, DFMW mode locking with switchable central wavelengths can also be obtained. It was further found that high pulse energy induced nonlinear effect of the dominant mode-locking mechanism transforming from DFMW to nonlinear Kerr beam cleaning effect(NL-KBC). The experimental results are valuable for further comprehending the dynamic characteristics of spatiotemporal mode-locked multimode fiber lasers, facilitating them much more accessible for applications.

CHARACTERIZATION OF SIGNAL CONDUCTIONALONG DEMYELINATED AXONS BY ACTION-POTENTIAL-ENCODED SECOND HARMONICGENERATION

Action-potential encoded optical second harmonic generation(SHG)has been recently proposedfor use in det ecting the axonal damage in patients with demnyelinat ing diseases.In this study,thecharact erization of signal conduction along axons of two different levels of denyelination wasstudied via a modified Hodgkin Huxley model,because some types of demyelinating disease,i.e.primary progressive and secondary progesive multiple scleross,are dificult to be distinguishedby magnetic resonance imaging(MRI),we focused on the diferences in signal conduction between two diferent demyelinated axons,such as the first-level demyelination and the second.level demyelination.The spatio-temporal distribution of action potentials along denyelinatedaxons and conduction properties including the refractory period and frequency encoding in theset wo patterns were investigated.The results showed that denyelination could induce the decreaseboth in the amplitude of action potentials and the ability of frequency coding,Furthermore,t hesignal conduction velocity in the second-level dernyelination was about 21%slower than that inthe first-level demyelination.The refractory period in the second-level demyelination was about32%longer t han the first-level.Thus,detecting the signal conduction in demnyelinat ed axons byaction-potential encoded optical SHG could greatly improve the assessment of demyelinatingdisorders to classify the patients.This technique also offers a potential fast and noninvasiveoptical approach for monitoring membrane potential.

DIAGNOSTIC APPLICATION OF MULTIPHOTON MICROSCOPY IN EPITHELIAL TISSUES

Epithelial cancer comprises more than 85%of human cancers.The detection and treatment at the early stage has been demonstrated to apparently improve patient survival.In this review,we summarize our recent research works on the diagnostic application of epithelial tissue based on multiphoton microscopy(MPM),including identification of the layered structures of esophagus,oral cavity,skin and bronchus tissues,establishment of the diagnostic features for distinguishing gastric normal tissue from cancerous tissue,linking collagen alteration and ectocervical epithelial tumor progression for evaluating epithelial tumor progression,and differentiating normal,inflammatory,and dysplastic ectocervical epithelial tissues.These results provide the groundwork for developing MPM into clinical multiphoton endoscopy.

NON-LINEAR SPECTRAL IMAGING MICROSCOPY STUDIES OF HUMAN HYPERTROPHIC SCAR

Skin scar is unique to humans,the major significant negative outcome sustained after thermal injuries,traumatic injuries,and surgical procedures.Hypertrophic scar in human skin is investigated using non-linear spectral imaging microscopy.The high contrast images and spectroscopic intensities of collagen and elastic fibers extracted from the spectral imaging of normal skin tissue,and the normal skin near and far away from the hypertrophic scar tissues in a 10-year-old patient case are obtained.The results show that there are apparent differences in the morphological structure and spectral characteristics of collagen and elastic fibers when comparing the normal skin with the hypertrophic scar tissue.These differences can be good indicators to differentiate the normal skin and hypertrophic scar tissue and demonstrate that non-linear spectral imaging microscopy has potential to noninvasively investigate the pathophysiology of human hypertrophic scar.

MULTIPHOTON MICROSCOPIC IMAGING OF MOUSE INTESTINAL MUCOSA BASED ON TWO-PHOTON EXCITED FLUORESCENCE AND SECOND HARMONIC GENERATION

Multiphoton microscopy(MPM),based on two-photon excited fuorescence and second harmonic generation,enables direct noninvasive visualization of tissue architecture and cell morphology in live tissues without the administration of exogenous contrast agents.In this paper,we used MPM to image the microstructures of the mucosa in fresh,unfixed,and unstained intestinal tissue of mouse.The morphology and distribution of the main components in mucosa layer such as columnar cells,goblet cells,intestinal glands,and a little collagen fibers were clearly observed in MPM images,and then compared with standard H&:E images from paired specimens.Our results indicate that MPM combined with endoscopy and miniaturization probes has the potential application in the clinical diagnosis and in vivo monitoring of early intestinal cancer.

RAMAN SPECTROSCOPY OF HUMAN HEMOGLOBIN FOR DIABETES DETECTION

Glycat ed hemoglobin(HbAlc)has been increasingly accepted as the gold standard for diabetesmonit oring.In this study,Raman spect roso was tentatively emplo yed for human hemoglobin(b)bioc hemical analysis aimed at de veloping a a simple blood test for diabetes monitoring.Ramanspectroscopy measurementsperformed oWereglobimples of patients(n=39)withconfirmed diabetes and healthyvolulhetentatiassignments of the measuredRaman bands were perfortwogegroups.Meanwhile,principal componentaminant analysis(LDA)wereemployed to develop effective weell1ormal controls andpatients with diabetes.Asat wo groups demonstrated twodistinct clust ers with a sensitivity and specificity d 73%,respectively.Then the effectiveness of the diagnostic algorithm based onechnique was confirmed by receiveroperating characteristic(ROC)curve.The area under the ROC curve was 0.92,indicating a good diagnostic result.In summary,our preliminary results demonstrate that proposing Raman spectroscopy can provide a significant potential for the noninvasive detection of diabetes.

NONLINEAR SPECTRAL IMAGING OF ELASTIC CARTILAGE IN RABBIT EARS

Elastic cartilage in the rabbit external ear is an important animal model with attractive potential value for researching the physiological and pathological states of cartilages especially during wound healing.In this work,nonlinear optical microscopy based on two-photon excited fluor-escence and second harmonic generation were employed for imaging and quantifying the intact elastic cartilage.The morphology and distribution of main components in elastic carti lage incuding cartilage cells,collagen and elastic fibers were clearly observed from the high-resolution two-di mensional nonlinear optical images.The areas of cell nuclei,a parameter related to the pathological changes of nornal or abnormal elastic cartilage,can be easily quantifed.Moreover,the three-dimensional structure of chondrocytes and matrix were displayed by constructing threedimensional image of cartilage tissue.At last,the enmission spectra from cartilage were obtained and analyzed.We found that the different ratio of collagen over elastic fibens can be used to locate the observed position in the elastic cartilage.The redox ratio based on the ratio of nicotinamide adenine dimucleotide(NADH)over flavin adenine dinucleotide(FAD)fuorescence can also be calculated to analyze the metabolic state of chondrocytes in different regions.Our results demonstrated that this technique has the potential to provide more accurate and comprehensive information for the physiological states of elastic cartilage.

DISTINGUISHING BETWEEN HYPERPLASTIC AND ADENOMATOUS POLYPS AND NORMAL COLONIC MUCOSA BY USING MULTIPHOTON LASER SCANNING MICROSCOPY

Precisely distinguishing between hyperplastic and adenomatous polyps and normal human colonic mucosa at the cellular level is of great medical significance.In this work,multiphoton laserscarming microscopy(MPLSM)was used to obtain the high.-contrast images and the morpho-logical characteristics from normal colonic mucosa,hyperplastic polyps and tubular adenoma.Byintegrating the length and area measurement tools and computing tool,we quantified thedifference of crypt morphology and the alteration of nuclei in normal and diseased human colonicmucosa.Our results demonstrated that the morphology of crypts had an obvious tendency tocystic dilatation or elongated in hyperplastic polyps and tubular adenoma.The cont ent andnumber of mucin droplets of the scattered goblet cells had a piecemeal reduction in hyperplastic polyps and a large decrease in tubular adenoma The nuclei of epithelial cells might be elongated and pseudostratified,but overt dysplasia was absent in hyperplastic polyps.Nevertheless,thenuclei showed enlarged,crowded,stratified and a rod-like structure,with loss of polarity intubular adenoma.These results suggest that MPLSM has the capacity to distinguish betweenhyperplastic and adenomat ous polyps and normal human colonic mucosa at the celular level.

Interstitial photoacoustic technique and computational simulation for temperature distribution and tissue optical properties in interstitial laser photothermal interaction

Interstitial laser immunotherapy(ILIT)is designed to use photothermal and immunological inter-actions for treatment of metastatic cancers.The photothermal ffect is crucial in inducing anti-tumorimmune responses in the host.Tissue temperature and tssue optical properties are important factorsin this process.In this study,a device combining interstitial photoacoustic(PA)technique andinterstitial laser photothermal interaction is proposed.Together with computational simulation,thisdevice was designed to determine temperature distributions and tissue optical properties during lasertreatment.Experiments were performed usinger-ivoFporcine liver tissue.Our results demonstratedthat interstitial PA signal amplitude was linearly dependent on tisue temperature in the tempera-ture ranges of 20-60℃,as wll as 65-80℃,with a dfferent slope,due to the change of tissue opticalproperties.Using the directly measured temperature in the tissue around the interstitial optical fiberdiffusion tip for calibration,the theoretical temperature distribution predicted by the bioheatequation was used to extract optical properties of tssue.Finally,the three-dimensional temperature distribution was simulated to guide tumor destruction and immunological stimulation,Thus,thisnovel device and method could be used for monitoring and controlling ILIT for cancer treatment.

Optical wavelength meter with machine learning enhanced precision

A photonic implementation of a wavelength meter typically applies an interferometer to measure the frequencydependent phase shift provided by an optical delay line.This work shows that the information to be retrieved is encoded by a vector restricted to a circular cone within a 3D Cartesian object space.The measured data belong to the image of the object space under a linear orthogonal map.Component impairments result in broken orthogonal symmetry,but the mapping remains linear.The circular cone is retained as the object space,which suggests that the conventional conic section fitting for the wavelength meter application is a premature reduction of the object space from R^(3)to R^(2).The inverse map,constructed by a learning algorithm,compensates impairments such as source intensity fluctuation and errors in delay time,coupler transmission,and photoreceiver sensitivity while being robust to noise.The simple algorithm does not require initial estimates for all parameters except for a broad bracket of the delay;further,weak nonlinearity introduced by uncertain delay can be corrected by a robust golden search algorithm.The phase-retrieval process is invariant to source power and its fluctuation.Simulations demonstrate that,to the extent that the ten parameters of the interferometer model capture all significant impairments,a precision limited only by the level of random noise is attainable.Applied to measured data collected from a fabricated Si_(3)N_(4)wavelength meter,greater than an order of magnitude improvement in precision compared with the conventional method is achieved.

Robust quantum secure direct communication with a quantum one-time pad over a collective-noise channel

We present two robust quantum secure direct communication (QSDC) schemes with a quantum one-time pad over a collective-noise channel. Each logical qubit is made up of two physical qubits and it is invariant over a collective-noise channel. The two photons in each logical qubit can be produced with a practically entangled source, i.e., a parametric down-conversion source with a beta barium borate crystal and a pump pulse of ultraviolet light. The information is encoded on each logical qubit with two logical unitary operations, which will not destroy the antinoise feather of the quantum systems. The receiver Bob can read out the sender's message directly with two single-photon measurements on each logical qubit, instead of Bell-state measurements, which will make these protocols more convenient in a practical application. With current technology, our two robust QSDC schemes are feasible and may be optimal ones.

Photonic cavity enhanced high-performance surface plasmon resonance biosensor

Herein we propose a novel strategy to enhance surface plasmon resonance(SPR)by introducing a photonic cavity into a total-internal-reflection architecture.The photonic cavity,which is comprised of a highly reflective photonic crystal(PC),defect layers,and a gold(Au)film,enables Fabry–Perot(FP)resonances in the defect layers and therefore narrows the SPR resonance width in the metallic surface as well as increases the electric field intensity and penetration depth in the evanescent region.The fabricated sensor exhibits a 5.7-fold increase in the figure of merit and a higher linear coefficient as compared with the conventional Au-SPR sensor.The demonstrated PC/FP cavity/metal structure presents a new design philosophy for SPR performance enhancement.

Magnetic spin–orbit interaction of light

We study the directional excitation of optical surface waves controlled by the magnetic field of light.We theoretically predict that a spinning magnetic dipole develops a tunable unidirectional coupling of light to transverse electric(TE)polarized Bloch surface waves(BSWs).Experimentally,we show that the helicity of light projected onto a subwavelength groove milled into the top layer of a 1D photonic crystal(PC)controls the power distribution between two TE-polarized BSWs excited on both sides of the groove.Such a phenomenon is shown to be solely mediated by the helicity of the magnetic optical field,thus revealing a magnetic spin-orbit interaction of light.Remarkably,this magnetic optical effect is clearly observed via a near-field coupler governed by an electric dipole moment:it is of the same order of magnitude as the electric optical effects involved in the coupling.This opens up new degrees of freedom for the manipulation of light and offers desirable and novel opportunities for the development of integrated optical functionalities.

Frequency-modulated continuous-wave dual-frequency LIDAR based on a monolithic integrated two-section DFB laser

We demonstrate a high-resolution frequency-modulated continuous-wave dual-frequency LIDAR system based on a monolithic integrated two-section(TS) distributed feedback(DFB) laser. In order to achieve phase locking of the two lasers in the TS-DFB laser, the sideband optical injection locking technique is employed. A high-quality linear frequency-modulated signal is achieved from the TS-DFB laser. Utilizing the proposed LIDAR system, the distance and velocity of a target can be measured accurately. The maximum relative errors of distance and velocity measurement are 1.6% and 3.18%, respectively.

Mode field switching in narrow linewidth mode-locked fiber laser

Acousto-optic interaction can be used for ultrafast optical field control in passively mode-locked fiber lasers.Here,we propose the use of an intracavity acousto-optic mode converter (AOMC) with combination of a few-mode fiber Bragg gratings (FM-FBG) to achieve narrow linewidth mode-locked pulse output with switchable transverse mode and wavelength in a ring fiber laser.Due to the selectivity of the FM-FBG to the input mode,the output mode and wavelength can be adjusted in the mode-locked fiber laser based on a semiconductor saturable absorption mirror.In experiments,by adjusting the acoustic frequency imposed in the AOMC,the wavelength of mode-locked pulses was switched from 1551.52 nm to 1550.21 nm,retaining the repetition rate of 12.68 MHz.At the same time,the mode conversion from the LP;to the LP;mode in the FM-FBG transmission port was achieved.This laser may find application in mode-division multiplexing systems.

Transient mode competition in directly modulated DFB semiconductor laser

A new effect of transient mode competition in directly modulated DFB laser based on equivalent phase-shift(EPS) technique is presented and studied. Since there are multi-order reflections in EPS structure and if the 0th order subgrating is properly designed, the transient lasing of 0th order will occur during the rising time of the injection current. As a result, transient mode competition between ?1st order(main mode) and 0th order will occur accordingly. This can consume redundant carrier and suppress the transient relaxation oscillation, which may be applied in some areas like on-off switching modulation of DFB semiconductor lasers. As an example, an equivalent ? phase shift(?-EPS) is carefully designed to realize the effect. In such a laser the 0th order wavelength is in the margin of the material gain region and the ?1st order wavelength is around the gain peak, while the stable single longitudinal mode(SLM) operation of the ?1st order is guaranteed. The simulation investigation is performed. Good results with suppressed relaxation oscillation and 1.25 Gb/s directly on-off modulation(32 d B extinction ratio) are demonstrated. We believe it provides a new kind of method for on-off switching with high extinction ratio and weak relaxation oscillation.