This study presents a dual-phase demodulation technique for multi-photon fluorescence microscopy system by extracting higher-order modulation signals. Results demonstrate a significant enhancement in the Signal-to-Background Ratio in Drosophila whole-brain samples. This study was also applied to neural dynamic observation in mouse brains.

In this article, we propose a novel method that integrates deep learning with Fabry-Perot liquid crystal (FP-LC) technology for fiber Bragg grating (FBG) interrogation. The use of FP-LC enhances the measurement range and enables high sensitivity in FBG sensors, making them appropriate for a wide range of applications requiring precise and responsive sensing. However, collecting a large amount of real experimental FBG sensor data is time-consuming, technically challenging, and resource-intensive. To address this issue, we utilize a conditional generative adversarial network (CGAN) to generate a sufficient amount of synthetic training data. The CGAN generates data conditioned on real FBG sensor data, ensuring that the generated data closely look like real experimental data distributions, which is crucial for effective model training. Moreover, we proposed a convolutional neural network (CNN) method to solve crosstalk problems, to improve sensing accuracy, and to precisely detect the peak wavelength of each FBG sensor. The experimental results demonstrated that the proposed CGAN technique effectively generates a large amount of data to improve the performance of the proposed CNN model. Furthermore, the results proved that the CNN trained on CGAN-generated data significantly improves the detection speed and accuracy of central wavelength measurements compared to traditional approaches. Hence, the proposed system is cost-effective, easy to set up for experiments, increases the feasibility and portability of modularization, fast and flexible, overcoming data shortages, and improving the sensing accuracy of wavelength detection for FBG sensor systems.

We demonstrate a novel approach combining two-photon microscopy with machine learning algorithms to analyze collagen organization in esophageal tissues, enabling differentiation between squamous cell carcinoma and high-grade dysplasia through quantitative extracellular matrix assessment. (c) 2025 The Author(s)

This study presents the liquid crystal Fabry–Pérot etalon (LC-FP) as the preferred laser wavelength tuning solution within a erbium-doped fiber ring laser architecture. The laser cavity wavelength can be adjusted by applying varying voltages to the LC-FP. Furthermore, tuning the laser wavelength can be facilitated by modifying the incident light through changes in the steering angle of the LC-FP, which is attributed to the angular dispersion characteristics of the device. The operational range for the steering angle of the LC-FP is ± 4 to 18 degrees. This architectural framework is adept at facilitating the generation of single-wavelength and dual-wavelength lasers within the C band. The tunable range for a single wavelength is approximately 13 nm, while the tunable range for dual wavelengths is around 14 nm, with a wavelength spacing of approximately 17.5 nm. These capabilities are primarily influenced by the operational wavelength of the erbium-doped fiber amplifier (EDFA), the operating wavelength of the collimator that directs the fiber optic beam into the LC-FP, and the fixed thickness of the LC-FP.

In this Letter, dynamic nano-thermal expansion images of reflective mirrors from high-intensity incident laser beams were observed in situ. The inspections are based on rapid 3D surface morphology changes on the reflective surfaces, captured by a Chromatic Confocal Microscope with Nanoscale Sensitivity (CCMNS). Nano-expansions of two types of coatings were studied: the E02 dielectric coating (coating 1) and the graphene-on-E02 complex film (coating 2), both applied to the same fused silica substrate. The superior thermal dissipation properties of coating 2, including enhanced heat dissipation, suppressed wavefront distortion, and its unique negative expansion coefficient, were observed. In addition to studying the effects of graphene coating, the CCMNS demonstrates an accurate and efficient approach for evaluating reflective mirrors. Moreover, the proposed methodology possesses enormous potential across various fields, ranging from estimating photonic elements dealing with high-intensity beams to physical thermal conductivity measurements.

The contrast or signal-to-noise ratio (SNR) in images is a crucial parameter that determines the quality of images in second harmonic generation laser scanning microscopy (SHG-LSM). With a better image contrast/SNR, SHG-LSM can be performed at a faster frame rate or deeper tissue locations without compromising image quality. In this work, we present a novel strategy based on the SHG signals of first-order modulation (1 M) to enhance the image contrast/SNR. Notably, a photodetector (i.e., photomultiplier tube) has a better signal SNR during the photon-to-electron conversion process at the frequency of 1 M, which is equivalent to the laser pulse repetition frequency. The improved signal SNR thus enhances the image quality, which agrees well with the results of the measured electrical spectra. A remarkable increment of image contrast by more than a factor of two has been obtained in images by using 1 M. In addition, the image acquisition time is also shortened by a factor of 2.5 compared to that for acquiring images with similar contrast taken without signal modulation. Furthermore, by analyzing the dependencies of image contrast/SNR on sample depth, we demonstrate that the images obtained with 1 M have better quality than those obtained without signal modulation at the same imaging depth.

Herein, we propose a pure optical design studying the spatial ion-distribution of organic films in light-emitting electrochemical cells, which can be further used to observe numerous ion-distributions inside organic/inorganic materials, Li-ion batteries, or micro-fluid channels.

In this study, we firstly propose an optical approach to investigate the ion profile of organic films in light-emitting electrochemical cells (LECs) without any invasive sputtering processes. In contrast to previous literatures, this pure optical strategy allows us to record clear and non-destructive ion profile images in the (Ru(dtb-bpy)3(PF6)2) consisted organic layer without interferences of complex collisions from the bombardment of secondary sputter induced ions in a conventional time-of-flight secondary ion mass spectrometry. By using the advanced position sensitive detector (PSD)-based Nanoscale Confocal Microscope, ion distribution profiles were successfully acquired based on the observation of nanoscale optical path length difference by measuring the refractive-index variation while the thickness of the LEC layer was fixed. Dynamic time-dependent ion profile displayed clear ion migration process under a 100 V applied bias at two ends of the LEC. This technique opens up a new avenue towards the future investigations of ion distributions inside organic/inorganic materials, Li-ion batteries, or micro-fluid channels without damaging the materials or disturbing the device operation.

We demonstrate a homebuilt confocal microscope with ∼60 nm axial resolution to visualize the optical path length (OPL) of liquid crystals (LCs) inside a 2-domain alignment LC cell. Since the microscope is sensitive to light polarization, it is capable of determining LC orientation by accounting for the OPL variation, ΔOPL. The resolution of birefringence depends on the measured ΔOPL from two cross-polarized channel detections, of which the concept is different from other polarization-resolved optical imaging techniques, but is relatively simple in optical layout and analysis. The different orientations of LCs and the voltage-dependent LC rotation properties in the 2-domain LC cell are monitored and analyzed. Additionally, the complicated LC orientation distribution at the junction of the two domains with different alignments can be clearly observed. It shows great possibilities of examining tissue birefringence related to disease progression and tiny birefringence variation of electro-optical materials under an external field, which are hardly resolved by conventional optical imaging techniques.

Engineered biomaterials provide unique functions to overcome the bottlenecks seen in biomedicine. Hence, a technique for rapid and routine tests of collagen is required, in which the test items commonly include molecular weight, crosslinking degree, purity, and sterilization induced structural change. Among them, the crosslinking degree mainly influences collagen properties. In this study, second harmonic generation (SHG) and coherent anti-Stokes Raman scattering (CARS) microscopy are used in combination to explore the collagen structure at molecular and macromolecular scales. These measured parameters are applied for the classification and quantification among the different collagen scaffolds, which were verified by other conventional methods. It is demonstrated that the crosslinking status can be analyzed from SHG images and presented as the coherency of collagen organization that is correlated with the mechanical properties. Also, the comparative analyses of SHG signal and relative CARS signal of amide III band at 1,240 cm(-1) to delta CH2 band at 1,450 cm(-1) of these samples provide information regarding the variation of the molecular structure during a crosslinking process, thus serving as nonlinear optical signatures to indicate a successful crosslinking.

We report a systematic study of the optical absorption of twisted bilayer graphene (tBLG) across a large range of twist angles from 0° to 30° using a high-resolution reflectance confocal laser microscopy (RCLM) system. The high-quality single crystalline tBLG was synthesized via the efficient plasma enhanced chemical vapor deposition techniques without the need of active heating. The sensitivity of acquired images from the RCLM were better than conventional optical microscopes. Although the highest spatial resolution of RCLM is still lower than scanning electron microscopes, it possesses the advantages of beam-damage and vacuum free. Moreover, the high intensity-resolution (sensitivity) images firstly allowed us to distinguish the slight absorption differences and analyze the correlation between the optical absorption and twisted angle of tBLG after data processing procedures. A maximum absorption (minimum transmission) was observed at the stacking angle of tBLG from 10° to 20°, indicating the interplay between the laser and the electron/hole van-Hove singularities when tBLG oriented around the critical angle (θc∼13°). The twisted angle correlated optical absorption paves an alternative way not only to visibly identify the interlayer orientation of tBLG but also to reflect the characterization of the interlayer coupling via its band structure.

Connective tissues in vertebrates consist of many anisotropic structures formed by collagen and muscle fibers, which could also generate intense second harmonic (SH). In SHG based tissue imaging, the incident light, when subjected to birefringence and scattering, would lead to a rapid decrement in imaging depth. The work simulating polarized light propagating through a thick and highly-scattering semi-infinite medium using a polarization-sensitive Monte Carlo model find that circular polarization would achieve deeper penetration depth. Henceforth, we use polarization engineered SHG imaging to investigate fish scales and pig tendon/dermis of various thickness, as well as the corresponding depolarization effect as a function of the imaging depth in this work. Critically, we have verified quantitatively the previous simulation results and presented the possibility to greatly improve the imaging of thick anisotropic and scattering tissues through engineering polarization. In parallel to wavefront shaping that uses a spatial light modulator or a wavefront sensor based deformable mirror to increase the signal-to-background (SBR) ratio in imaging, our approach is simple, effective, and sensitive to tissue anisotropy.

Based on a rigid square fiber for wave vector delivery, we present a novel (to the best of our knowledge) wave-vector-encoded nonlinear-optical endomicroscopy (WENE). WENE overcomes three tangled issues, including femtosecond pulse broadening induced signal degradation, complexity of packaging miniaturized scanners in the distal end, and pixel-like images, which cannot be fully addressed by current distal scanning nonlinear endomicroscopy (NE) or fiber-bundle-based proximal scanning NE. Due to the advantages of its simplicity in overall configuration and package in the distal end, the capability of addressing the issue of pulse broadening, and offering continuous wave vector delivery, the demonstrated WENE shows great promise for future basic research on biomedical processes and minimally invasive utilization for clinical diagnosis.

A quantitative analytical method to discriminate among the various types of cancerous esophagus tissue is essential for accurate cancer staging. This paper reports on the use of ratiometric nonlinear optical microscopy to reveal the ratio of two-photon excited fluorescence (TPEF) to second harmonic generation (SHG) and forward to backward (F/B) SHG from single collagen fibers only in submucosa of esophageal squamous cell carcinoma. This makes it possible to accurately differentiate among the four stages of esophageal cancer, providing results that are in good agreement with histopathology. Furthermore, it is confirmed by polarization-dependent SHG that the varied SHG response in esophageal cancer tissues is mainly from the shrinkage in diameter of collagen fibers instead of the collagen triple helixes altered by cancer cells. Based on the results of TPEF/SHG and F/B SHG ratio, they can cooperatively improve the precision of diagnostics on esophageal cancer and could be transferred to other types of cancer diseases with changed collagen fibers. Impact statement The issue of classifying esophageal cancer at various developmental stages is crucial for determining the optimized treatment protocol for the patients, as well as the prognosis. Precision improvement in staging esophageal cancer keeps seeking quantitative and analytical imaging methods that could augment histopathological techniques. In this work, we used nonlinear optical microscopy for ratiometric analysis on the intrinsic signal of two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) from single collagen fibers only in submucosa of esophageal squamous cell carcinoma (ESCC). The blind tests of TPEF/SHG and forward (F)/backward (B) SHG were demonstrated to compare with the histology conclusion. The discussion of sensitivity and specificity was provided via statistical comparison between the four stages of esophageal cancer. To the best of our knowledge, this is the first study of using these two ratios in combination for staging ESCC.

This work describes non-invasive observations of dynamic thermal lensing in an end-pumped Nd:YVO4 laser. Measurements were obtained with a nanoscale optical ruler created using chromatic aberrations, pinholes, dispersive gratings, and position-sensitive detectors. This study reports on variations in thermally induced oscillations and on underdamping behavior in the regime of high pump power. Dynamic data related to the thermal behavior can be used to study the balance between driving forces (pumping and thermal stresses) and damping losses (cooling and output coupling). The non-invasive nature of the proposed scheme along with its sub-100-nm axial resolution, sub-millisecond time resolution, and simple configuration makes it widely applicable for studying heat-related phenomena within laser crystals. The preliminary results show that such non-invasive methods could be used to detect thermally induced nanoscale deformations in integrated circuits, high-power optoelectronic devices, and optical devices with high-power illumination.

Pulsed lasers can be utilized to generate intensity-modulated light at the fundamental frequency of the laser repetition rate as well as higher order modulation (HOM) frequencies in the recent study. We also demonstrated the feasibility of using pulse lasers and fiber-wavelength-convertors as a light source in multicolor frequency-domain (FD) biophotonic systems. In this paper, we present a novel approach to enhancing the intensity of signals below 1 GHz in HOM-based FD systems simply by employing the fiber dispersion effect. The energy spectrum of HOMs can be redistributed to enhance the intensity of HOMs within the bandwidth of the photo-detector without the need for an external (optical or electrical) amplifier. We also demonstrate that the length of dispersive fiber can be optimized via numerical calculations, the results of which are in good agreement with experimental measurements. Finally, we demonstrate a frequency-domain-photon-migration system employing the fiber dispersion effect to enhance sub-GHz signals at a wavelength of 1.03 μm in order to recover the optical properties of turbid samples. Our measurements results demonstrate the superiority of the proposed FD source over the conventional directly modulated FD light source. Furthermore, the simple configuration of the proposed scheme makes it applicable to a wide range of FD biophotonic systems.

In this study, a Q-switch pumped supercontinuum laser (QS-SCL) is used as a light source for in vivo imaging via ultrahigh-resolution optical coherence tomography and angiography (UHR-OCT/OCTA). For this purpose, an OCT system based on a spectral-domain detection scheme is constructed, and a spectrometer with a spectral range of 635 - 875 nm is designed. The effective full-width at half maximum of spectrum covers 150 nm, and the corresponding axial and transverse resolutions are 2 and 10 µm in air, respectively. The relative intensity noise of the QS-SCL and mode-locked SCL is quantitatively compared. Furthermore, a special processing algorithm is developed to eliminate the intrinsic noise of QS-SCL. This work demonstrates that QS-SCLs can effectively reduce the cost and size of UHR-OCT/OCTA instruments, making clinical applications feasible.

An advanced confocal microscope with nanoscale depth resolutions and the capability for rapid capture of 3D surface topography was presented. The proposed microscope shows great promise for optical testing of electronic or photonic elements.

Elimination of virus-carried insects, such as mosquitoes, by an efficient method is of primary importance to preventing the dissemination of infectious diseases and consequentially reducing the health and financial burden on human society. Research herein entails the design, characterization, and implementation of a structurally simple and cost-effective electro-optical system for mosquito-hunting, which is optimized with a system response time under 1.25 ms considering the average mosquito flight speed of 0.2777 m/s, capable of locating the free-flight adult mosquito and knocking it down, synchronously, without any post data-processing. Empirically, the visible-near-infrared absorption spectra of three mosquito species, namely, Culex piplens molestus, Aedes albopictus, and Armigeres subalbatus, were acquired to examine the disparity in photo-absorption property among different mosquito species and help determine an optimal wavelength for injuring the insects. Armigeres subalbatus, a natural transmission vector of filariasis to humans, was employed for the evaluation of the system's efficacy. By introducing a free-flight mosquito about 20 cm in front of an dichroic mirror that combines two optical beams for detection and eradication, a dynamically tracking photonic antenna with a maximal area of 45 mm by 39 mm can continuously track the insect and then knock it down by an instant exposure of a lethal beam with average energy ranging from 75 mJ to 155 mJ. Moreover, the dependence of the fate of the insects on the lethal beam energy dosage is statistically assessed. Overall, this research has successfully demonstrated the concept of the synchronizing scheme of identification and eradication with over 60% of mortality rate once the energy dosage is increased above 75mJ, and may be applicable to the control of other insects or avian animals. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Yi-Sheng Lin1, Ming-Che Chan2, Fu-Jen Kao3 and Guan-Yu Zhuo4,5,* 1Institute of Lighting and Energy Photonics, College of Photonics, National Chiao-Tung University, No. 301, Gaofa 3rd Rd., Guiren Dist., Tainan 711, Taiwan 2Institute of Photonic System, College of Photonics, National Chiao-Tung University, No. 301, Gaofa 3rd Rd., Guiren Dist., Tainan 711, Taiwan 3Institute of Biophotonics, National Yang-Ming University, No. 155, Sec. 2, Linong St., Taipei 112, Taiwan 4Institute of New Drug Development, China Medical University, No. 91, Xueshi Rd., North Dist., Taichung 404, Taiwan 5Integrative Stem Cell Center, China Medical University Hospital, No. 2, Yude Rd., Taichung 404, Taiwan E-mail: zhuo0929@mail.cmu.edu.tw