Path Difference Research Articles

Chromatic dispersion measurement of optical fiber using spectroscopic optical coherence tomography

Chromatic dispersion (CD) in optical fibers results in the broadening and overlapping of transmitted lights, and thus reduces the capacity of information transmission and increases the bit-error-rate of communication system. Hence it needs to be accurately measured and then compensated. There have been various methods for fiber CD measurement, but most of them are complicated to obtain wavelength components and require adjustment during measurement, and thus have the drawbacks of being time-consuming, and susceptible to system stability and environmental influences. In this work, a measurement method of fiber CD based on the principle of spectroscopic optical coherence tomography (OCT) was proposed by using a swept-source OCT system to capture interference signal, and using Wigner-Villy distribution as time-frequency analysis method to extract spectral − spatial distribution. Wavelength − OPD curve could be obtained from the distribution, where the OPD (optical path difference) is the spatial delay induced by the fiber CD, and the CD profile varying with the wavelength was finally obtained from the curve. One fiber sample was measured with 1060 and 1310 nm band systems, and another different type of fiber sample was measured with 1310 nm band system. The measured results are agreement with the claimed or theoretical results, demonstrating the feasibility of this method. It has some significant advantages and is a promising method for fiber CD measurements.

Capturing the Interplay Between TADF and RTP Through Mechanically Flexible Polymorphic Optical Waveguides

AbstractPolymorphism plays a pivotal role in generating a range of crystalline materials with diverse photophysical and mechanical attributes, all originating from the same molecule. Here, we showcase two distinct polymorphs: green (GY) emissive and orange (OR) emissive crystals of 5′‐(4‐(diphenylamino)phenyl)‐[2,2′‐bithiophene]‐5‐carbaldehyde (TPA‐CHO). These polymorphs display differing optical characteristics, with GY exhibiting thermally activated delayed fluorescence (TADF) and OR showing room temperature phosphorescence (RTP). Additionally, both polymorphic crystals display mechanical flexibility and optical waveguiding capabilities. Leveraging the AFM‐tip‐based mechanophotonics technique, we position the GY optical waveguide at varying lengths perpendicular to the OR waveguide. This approach facilitates the exploration of the interplay between TADF and RTP phenomena by judiciously controlling the optical path length of crystal waveguides. Essentially, our approach provides a clear pathway for understanding and controlling the photophysical processes in organic molecular crystals, paving the way for advancements in polymorphic crystal‐based photonic circuit technologies.

Capturing the Interplay Between TADF and RTP Through Mechanically Flexible Polymorphic Optical Waveguides.

Polymorphism plays a pivotal role in generating a range of crystalline materials with diverse photophysical and mechanical attributes, all originating from the same molecule. Here, we showcase two distinct polymorphs: green (GY) emissive and orange (OR) emissive crystals of 5'-(4-(diphenylamino)phenyl)-[2,2'-bithiophene]-5-carbaldehyde (TPA-CHO). These polymorphs display differing optical characteristics, with GY exhibiting thermally activated delayed fluorescence (TADF) and OR showing room temperature phosphorescence (RTP). Additionally, both polymorphic crystals display mechanical flexibility and optical waveguiding capabilities. Leveraging the AFM-tip-based mechanophotonics technique, we position the GY optical waveguide at varying lengths perpendicular to the OR waveguide. This approach facilitates the exploration of the interplay between TADF and RTP phenomena by judiciously controlling the optical path length of crystal waveguides. Essentially, our approach provides a clear pathway for understanding and controlling the photophysical processes in organic molecular crystals, paving the way for advancements in polymorphic crystal-based photonic circuit technologies.

Highly sensitive CH4-TDLAS sensor based on 3D-printed multi-pass cell

In this paper, a highly sensitive methane (CH4) sensor based on tunable diode laser absorption spectroscopy (TDLAS) with 3D-printed multi-pass cell (MPC) is reported. A MPC design model based on ray tracing mathematical method with the law of reflection in vector form was established. The designed MPC has an optical path length (OPL) of 37.8 m and a ratio of optical path length to volume (RLV) of 13.9 cm−2 to enhance the optical absorption. The 3D-printed gas chamber equipped with the MPC and fiber-coupled input greatly simplifies optical alignment. A minimum detection limit (MDL) of the constructed CH4-TDLAS sensor based on fiber-coupled 3D-printed MPC with dense spot pattern was determined to be 30.93 ppb. It can be further improved to 11.79 ppb when the averaging time of the system was 300 s according to the Allan deviation analysis.

Clinical outcomes after topography-guided FS-LASIK for myopia with nonastigmatic eyes

BackgroundTo analyze the clinical outcomes after topography-guided femtosecond laser–assisted laser in situ keratomileusis (FS-LASIK) with Phorcides Analytic Engine (PAE) algorithm or Custom-Q FS-LASIK for myopia with nonastigmatic eyes.MethodsIn this retrospective study, a total of 90 eyes with myopia without manifest astigmatism (82 patients) were included. All surgeries were performed by topography-guided FS-LASIK planned with a PAE algorithm (42 eyes) or Custom-Q system (48 eyes). Refractive, visual outcomes and corneal aberrations were compared between the two groups.ResultsAt 6 months postoperatively, the postoperative uncorrected distance visual acuity (UDVA) was 20/20 or better in 42 eyes (100%) in the PAE compared with 44 eyes (92%) in Custom-Q (P = .120). The postoperative UDVA of 20/16 or better was measured in 92% of eyes in the PAE group and 81% of eyes in the Custom Q group (P = .320). Postoperative corrected distance visual acuity, manifest refractive spherical equivalent and refractive astigmatism were similar between the two groups (P > .05). The postoperative optical path difference (OPD) and Strehl ratio (SR) were significantly better in the PAE group compared with the Custom Q group.ConclusionsTopography-guided FS-LASIK with PAE algorithm or Custom Q demonstrated similar refractive efficacy and predictability. PAE for the patients with zero manifest astigmatism demonstrated better results in correcting corneal aberrations.

Vibration-Induced Sweeping Operation in Fiber Lasers

A new vibration-based mechanism of optical frequency/wavelength sweeping in fiber lasers induced by optical path length modulation of a laser cavity section is proposed. The mechanism is implemented for an erbium-doped fiber ring laser with a saturable absorber. Without the vibrations, the laser generates a single longitudinal mode (SLM) radiation. We show experimentally for the first time that mechanical vibrations of the laser cavity section can lead to mode dynamics in both frequency and time domains. The possibility of obtaining various mode dynamics, such as vibration-induced sweeping in a wavelength range of up to 2.2 nm or SLM generation with periodic mode hopping between two fixed longitudinal modes depending on the pump wavelength, is experimentally shown. In this vibration-based approach, the interval between changes in the laser cavity modes has good stability, because it directly relates to the vibration period.

Comparative characterization of fatty acids and volatile substances in Chinese indigenous and hybrid pork in raw, cooked, and reheated states

Fatty acids and volatile substances in hybrid pork (Duroc × Landrace × Yorkshire; DLY) and four indigenous pork (Guangdong small-ear spotted; hill black; Beijing black, BB; and Qingyu) in raw, cooked, and reheated states were explored. The objectives were to determine odor differences between DLY and indigenous pork and the difference in changes after heating and reheating and to clarify the reasons for these changes. Results revealed that C18:1 and C20:4 fatty acids are the key to distinguishing DLY pork from indigenous pork. After cooking, the greatest decrease was observed in the proportion of polyunsaturated fatty acids in pork, and after reheating, monounsaturated fatty acids were detected, except in the BB pork. The substances that accounted for the difference between DLY and indigenous pork were 2,3-octadione, hexanal, 1-octen-3-ol, 2-nonanone (after heating), and (Z)-2-nonenal (after reheating). Reheating reduced the content of nonanal, 2,3-octandione, hexanal, and (E,E)-2,4-decadienal, resulting in the deterioration of the aroma. In the DLY pork, the dramatic increase in the (Z)-2-nonenal content may be the key factor. Principal component analysis identified that the difference in aroma between DLY and indigenous pork increased after reheating, but hierarchical cluster analysis showed that regardless of treatment, flavor difference was smaller between DLY and indigenous pork than among indigenous pigs. The analysis results show that differences in fatty acid content and oxidation path in unsaturated fatty acids were the reasons for the difference in aroma and the deterioration of flavor after reheating.

Optical path length difference of ray paths inside a reference sphere: a new approach for determining wavefront aberrations in axially symmetrical systems with an object at infinity

A new, to the best of our knowledge, method is proposed to analyze the wavefront aberrations in an axially symmetrical system with an object at infinity. The study commences by determining the optical path length (OPL) difference between two ray paths from the object to the reference sphere. The proposed method is then used to explore the claim in J. Opt. Soc. Am. A 19, 1187 (2002)JOAOD60740-323210.1364/JOSAA.19.001187 that wavefront aberrations do not depend on the radius of the reference sphere. It is found that this claim does not hold when the image plane is non-Gaussian. The proposed approach is applied to determine the primary wavefront aberrations of an axially symmetrical system with an object at infinity. The numerical values of the primary aberrations (spherical, coma, astigmatism, and field curvature) are in excellent agreement with those determined by Zemax simulations. The superiority of the proposed method over Zemax in determining the distortion aberration is confirmed through raytracing. Overall, the proposed method provides a useful contribution to the development of optical systems for applications requiring high-resolution imaging.

A self-powered photoelectrochemical and non-enzymatic glucose sensor based on ERGO/ZnONWs/CdS photoanode

We have developed an efficient, self-powered, non-enzymatic photoelectrochemical (PEC) glucose sensor operating in the visible spectrum. The sensor is based on electrochemically reduced graphene oxide (ERGO) and zinc oxide (ZnO) nanowalls (NWs) decorated with cadmium sulfide (CdS) quantum dots (QDs). We used a one-pot electrochemical process to grow vertically aligned ZnONWs on ERGO, followed by using the sequential ionic layer adsorption and reaction (SILAR) technique to decorate the ZnONWs with CdS QDs. The resulting ERGO/ZnONWs/CdS photoelectrode exhibits a three-dimensional hierarchical morphology, providing a large surface area for enhanced surface-substrate interactions and increased optical path length, leading to high absorptivity at visible light. Under one solar light illumination without a bias voltage, the electrode generated a significantly higher photocurrent density (1150 µAcm-2) in the presence of glucose (15.00 mM) than in the absence of glucose (150 µAcm-2). As a PEC glucose sensor, the ERGO/ZnONWs/CdS photoelectrode demonstrated two linear correlations in the glucose concentration range of 0.01–1.00 mM and 1.00–15.00 mM. The sensor has 430.06 and 25.75 µA cm-2mM-1 sensitivities and a low detection limit (1.1 µM). This novel visible light-mediated self-powered electrochemical sensing platform is cost-effective, reproducible, and stable for non-enzymatic glucose detection.

Fast and direct calibration for high numerical aperture quadriwave lateral shearing interferometry using geometry model with higher-order Taylor expansion

The current research on quadriwave lateral shearing interferometry (LSI) is primarily focused on the measurements of plane wave or quasiplane wave. When directly measuring spherical waves with high numerical apertures (NA>0.35), it will generate additional systematic errors, which affect measurement accuracy. To make the quadriwave LSI applicable to the measurements of a high-NA spherical wave, this paper proposes a fast and direct calibration method by establishing the geometry model of the quadriwave LSI with high-NA spherical wave incidence. The expression for the optical path difference represented systematic errors introduced by high-NA spherical waves in the shearing wavefronts are derived, which utilize a ninth-order Taylor expansion and Zernike polynomials fitting to achieve the high accuracy required by the high-NA spherical wave incidence. Then, the systematic errors are directly calibrated in the shearing wavefronts of four directions. This paper presents the theoretical analysis and verifies the feasibility and reliability of the proposed method through simulations and experiments, achieving a good measurement accuracy.

Correcting Optical Aberration via Depth-Aware Point Spread Functions.

Optical aberration is a ubiquitous degeneration in realistic lens-based imaging systems. Optical aberrations are caused by the differences in the optical path length when light travels through different regions of the camera lens with different incident angles. The blur and chromatic aberrations manifest significant discrepancies when the optical system changes. This work designs a transferable and effective image simulation system of simple lenses via multi-wavelength, depth-aware, spatially-variant four-dimensional point spread functions (4D-PSFs) estimation by changing a small amount of lens-dependent parameters. The image simulation system can alleviate the overhead of dataset collecting and exploiting the principle of computational imaging for effective optical aberration correction. With the guidance of domain knowledge about the image formation model provided by the 4D-PSFs, we establish a multi-scale optical aberration correction network for degraded image reconstruction, which consists of a scene depth estimation branch and an image restoration branch. Specifically, we propose to predict adaptive filters with the depth-aware PSFs and carry out dynamic convolutions, which facilitate the model's generalization in various scenes. We also employ convolution and self-attention mechanisms for global and local feature extraction and realize a spatially-variant restoration. The multi-scale feature extraction complements the features across different scales and provides fine details and contextual features. Extensive experiments demonstrate that our proposed algorithm performs favorably against state-of-the-art restoration methods.

A hybrid learning approach to better classify exhaled breath's infrared spectra: A noninvasive optical diagnosis for socially significant diseases.

Early diagnosis is crucial for effective treatment of socially significant diseases, such as type 1 diabetes mellitus (T1DM), pneumonia, and asthma. This study employs a diagnostic method based on infrared laser spectroscopy of human exhaled breath. The experimental setup comprises a quantum cascade laser, which emits in a pulsed mode with a peak power of up to 150 mW in the spectral range of 5.3-12.8 μm (780-1890 cm-1), and a Herriott multipass gas cell with a specific optical path length of 76 m. Using this setup, spectra of exhaled breath in the mid-infrared range were obtained from 165 volunteers, including healthy individuals, patients with T1DM, asthma, and pneumonia. The study proposes a hybrid approach for classifying these spectra, utilizing a variational autoencoder for dimensionality reduction and a support vector machine method for classification. The results demonstrate that the proposed hybrid approach outperforms other machine learning method combinations.

Whole-field principal angle and optical path retardation measurements using white light OPD scanning polariscope with first moment algorithm

White-light Optical Path Difference (OPD) scanning polariscope is currently an accepted technique for analyzing photoelastic specimens. While it has proven effective in overcoming limitations associated with phase-stepping and fringe scanning techniques, it is constrained when evaluating optical path retardation smaller than the light source coherence length. To address this limitation, a white-light OPD scanning polariscope, equipped with a first moment algorithm, has been introduced for the comprehensive examination of whole-field principal angle and optical path retardation. This article demonstrates the design and operational principles of the proposed polariscope, details an experimental setup for its deployment, and presents findings from practical applications of this setup. The results confirm the effectiveness and practicality of the proposed polariscope. Furthermore, these results highlight its precision, with standard deviations of 0.176° for principal angle and 6.4 nm for optical path retardation measurements.

Achievement splitting for topological states with pseudospin in phase modulation by using gyromagnetic photonic crystals

As we know, valley-Hall kink states or pseudospin helical edge states are excited by polarized-momentum-locking [left-handed circular polarization (LCP) and right-handed circular polarization (RCP)] because the valley-Hall kink modes or pseudospin polarized modes have intrinsic and local chirality, which is difficult for these states to achieve phase modulation. Here we theoretically design and study a compatible topological photonic system with coexistence of photonic quantum Hall phase and pseudospin Hall phase, which is composed of gyromagnetic photonic crystals with a deformed honeycomb lattice containing six cylinders. A typical kind of hybrid topological waveguide states with pseudospin-characteristic, magnetic field-dependent, and strong robustness against backscattering and perfect electric conductor (PEC) is realized in the present system. Furthermore, we re-design a structure with intersection-liked, achieve splitting for one-way pseudospin quantum Hall edge states by using phase modulation. Robustness of the one-way pseudospin-quantum Hall edge states in splitting has been demonstrated as well. Additionally, PEC inserted in transport channel brings optical path difference in waveguide transmission, which would influence splitting for hybrid topological waveguide states in phase difference modulation. This work not only provides a new way for manipulation (i.e., phase modulation) of hybrid topological waveguide states in compatible topological photonic system from distinct topological classes but also has potential in various applications, such as sensing, signal processing, and on-chip communications.

Residual path integrals for re‐rendering

AbstractConventional rendering techniques are primarily designed and optimized for single‐frame rendering. In practical applications, such as scene editing and animation rendering, users frequently encounter scenes where only a small portion is modified between consecutive frames. In this paper, we develop a novel approach to incremental re‐rendering of scenes with dynamic objects, where only a small part of a scene moves from one frame to the next. We formulate the difference (or residual) in the image between two frames as a (correlated) light‐transport integral which we call the residual path integral. Efficient numerical solution of this integral then involves (1) devising importance sampling strategies to focus on paths with non‐zero residual‐transport contributions and (2) choosing appropriate mappings between the native path spaces of the two frames. We introduce a set of path importance sampling strategies that trace from the moving object(s) which are the sources of residual energy. We explore path mapping strategies that generalize those from gradient‐domain path tracing to our importance sampling techniques specially for dynamic scenes. Additionally, our formulation can be applied to material editing as a simpler special case. We demonstrate speed‐ups over previous correlated sampling of path differences and over rendering the new frame independently. Our formulation brings new insights into the re‐rendering problem and paves the way for devising new types of sampling techniques and path mappings with different trade‐offs.

Influence of biceps-triceps ratio on golf swing performance.

This study examines how maintaining a straight leading arm affects the muscle strength balance between the biceps and triceps in golfers and its influence on golf performance. We recruited 20 male participants aged 18-45, including 10 golfers and 10 non-golfers. The participants' average age was 25.6±6.2 years, height 1.8±0.07 m, and weight 75.6±10.2 kg. We measured isometric and isokinetic muscle strength using the Primus RS Dynamometer (BTE Technologies, Hanover, MD, USA) and assessed golf swing performance with the Optishot 2 Golf Simulator (Optishot, Brighton, MI, USA). Golfers exhibited significantly greater triceps strength (P = 0.02) and a lower biceps-to-triceps strength ratio (P = 0.002) than non-golfers. Low-handicap golfers showed more centered and consistent ball impacts compared to mid-handicap golfers. There were no significant differences in swing path and face angles between low- and mid-handicap golfers. Muscle strength and the biceps-to-triceps strength ratio correlated with driving distance, as well as the frequencies of specific swing paths, face angles, and ball impact points, highlighting the complex interplay between muscle balance and swing performance. Greater triceps strength and a lower biceps-to-triceps strength ratio are key for maintaining a straight leading arm, especially in skilled golfers. While increased muscle strength tends to enhance driving distance, it does not necessarily improve accuracy. Consistent ball impact points may indicate higher skill levels. Future research should involve a larger, more diverse participant pool to validate these findings and further explore the complex nature of golf swing performance.

Direct search or remote search? Export market expansion path for firms in underdeveloped areas - evidence from the five cities of the Hexi Corridor, China

ABSTRACT The expansion of firms’ export markets is crucial for their own growth and local economic growth. Studies suggest two market expansion modes: direct search and remote search. However, research often overlooks underdeveloped areas and the influence of firm heterogeneity. Using data from China Customs Database and CEPII Database, this article investigates the export market expansion patterns of firms in underdeveloped regions. The study focuses on five specific cities in the Hexi Corridor, a representative underdeveloped region in western China. The results show that firms in underdeveloped areas mainly follow the remote search path during their export market expansion. The likelihood of success in entering new target markets is significantly influenced by the similarity between the target market and their existing markets, while the geographical distance between trade partners has little effect. Additionally, there are significant differences in the market expansion path of different types of firms. Private-owned enterprises demonstrated a greater reliance on the remote search mode than state-owned enterprises, collective-owned enterprises and Sino-foreign joint ventures. It may stem from their limited ability to access resources and policy support.

A three-degrees-of-freedom motion error measurement system based on Mach–Zehnder interferometry

This paper proposes a three-degree-of-freedom motion error measurement system based on Mach–Zehnder interferometry. The system consisted of an optical flat, beam-splitting prisms, and a reflector. When the stage was moving, the straightness error of the linear guides changed the optical path difference, which in turn caused a phase shift in the interferogram. This phase shift could be calculated by utilizing an image processing algorithm that was also developed during this study. The 3-DOF straightness errors, which included one linear error and two angular errors could be calculated. A commercial laser interferometer and a chromatic confocal sensor were used as reference sensors. The experimental results showed that the linear and angular measurement errors of the system were within ± 0.05 μm and ± 0.3″, respectively over measurement ranges of 100 mm and 60″. The repeatability, which was expressed by the standard deviation, was within 40 nm and 0.3″ for the linear and angular measurements, respectively. The proposed Mach-Zehnder interferometer has been successfully applied in a high-accuracy 3D surface topographic measurement system. It was able to effectively compensate the motion error and improve the accuracy for surface profiling.

Symmetric optical multipass matrix systems and the general rapid design methodology

We proposed an original type of multipass cell named symmetric optical multipass matrix system (SMMS), in which the same matrix patterns of various sizes can be formed on both sides. According to its special symmetric configurations, the SMMS design problem is modeled as a variant of the classical traveling salesman problem, which can be rapidly solved by evolutionary optimization algorithms. Two sets of 3-mirror SMMSs are designed, analyzed and built, which show superior characteristics of high stability, desirable beam quality and adjustable optical path lengths. Additionally, they can support simultaneous detection of multiple species with multi-laser channels. The proposed method is further extended to design a 4-mirror SMMS, which verifies the universality and robustness of the design methodology. The experimental observations are in consistent with the theoretical calculations. The newly proposed SMMSs have a broad application prospect in trace gas measurement.

Dynamic spectral extraction method with approximately the same optical path length of non-invasive quantitative analysis of human blood components

The non-invasive quantitative analysis of blood components using spectroscopic methods based on Beer-Lambert law, and dynamic spectroscopic theory needs to meet the four applicable conditions of this law. However, in practical applications, due to the scattering characteristics of human tissue, it is difficult to meet the two conditions (parallel monochromatic light and non-scattering homogeneous system of absorbing substances), which will reduce the accuracy of quantitative analysis. To reduce the principle error caused by scattering, this paper proposes an extraction method for dynamic spectra with approximately the same optical path length. This method extracts approximately the same absorbance values from photoplethysmographic (PPG) spectral signals. A smaller absorbance value corresponds to a thinner blood layer, in which light can be approximated as parallel light, thus maximizing the satisfaction of the conditions of Beer-Lambert law. In the experimental, compared with the traditional single-edge extraction method, the proposed method has higher prediction accuracy. The correlation coefficients of the total cholesterol and triglycerides increased by 31.22% and 38.05%, and the root mean square errors decreased by 29.63% and 37.14%. The results show that the methods can significantly enhance the robustness of non-invasive quantitative analysis of blood components based on dynamic spectral theory.