Optical Path Research Articles

The Microscopic World: Deign and Construction a Low-cost, Portable Reflective Digital Holographic Microscope

In daily life, scratches are often left on reflective surfaces, including rearview mirrors, makeup mirrors, and optical lenses, posting significant problems on image quality. Traditional 3D measurement methods usually use expensive and massive instruments, such as confocal microscopes or electron microscopes, which are not practical for high school research projects. Digital microscopy has the advantages of being non-contact, full-field, real-time, and high-precision, offering a solution. Therefore, this paper explores the use of digital holographic microscopy to measure the 3D surface of reflective surfaces. The study is based on a Michelson interferometer, reducing the systems size by using folded optical path and eliminating unnecessary converging lenses. Through simulation experiments, this research explores how various optical system parameters affect imaging quality and optimizes the clarity of the 3D reconstruction. Based on the conclusions from the simulations, hardware set-up of the system was selected, including a 635nm laser, collimation lenses, a beam splitter, mirrors, and a CMOS camera, keeping the total cost under 3000 yuan. In the experimental section, the system was built, and through adjustments in the reference beam angle and the distance between the object and the camera, clear interference fringes were successfully obtained. To further enhance the research, MATLAB was used to write an angular spectrum diffraction reconstruction algorithm. The experiments conducted on lenses and wafers produced their 3D profiles. This research demonstrates the potential of digital microscopy in both solving real-world problems and helping high school students explore the field of physics, promoting a deeper understanding of concepts like optical interference and diffraction

Picometer sensitive prototype of the optical truss interferometer for LISA

Abstract The optical truss interferometer (OTI) is a contingent subsystem proposed for the LISA telescopes to aid in the verification of a 1 pm Hz optical path length stability. Each telescope would be equipped with three pairs of compact fiber-coupled units, each forming an optical cavity with a baseline proportional to the telescope length at different points around the aperture. Employing a Pound–Drever–Hall approach to maintain a modulated laser field on resonance with each cavity, the dimensional stability of the telescope can be measured and verified. We have designed and developed prototype OTI units to demonstrate the capability of measuring stable structures, such as the LISA telescope, with a 1 pm Hz sensitivity using a set of freely mountable fiber-injected cavities. Aside from its initial motivation for the telescope, the OTI can also be readily integrated with other systems to aid in ground testing experiments. In this paper, we outline our experimental setup, measurement results, and analyses of the noise limitations.

Aberration analysis of reflective and transmissive type optical spectrometer using Zemax

This study presents a detailed analysis of geometrical aberrations in reflective and transmissive optical spectrometers using Zemax optical design software. Wavefront aberration, a standard metric for assessing geometrical aberration in optical systems, is employed to evaluate performance. Spectrometers are designed in sequential mode and analyzed with the physical optics propagation (POP) algorithm. Key performance metrics, such as optical path difference (OPD), transverse ray plot, spot diagram, modulation transfer function (MTF), and geometric encircled energy, are used to assess the spectrometers. This analysis aims to study aberration effects that cause distorted and blurry spectra, ultimately impacting spectrometer accuracy and efficiency. A comparative analysis of both spectrometers in the visible range for zero and first-order diffraction grating is reported. Line and edge spread functions are simulated to examine the spectrometer’s resolution capability. This study comprehensively compares optical spectrometers, highlighting their applicability across various fields.

Resolving Artifacts and Improving the Detection Limit in Circular Differential Scattering Measurement of Chiral and Achiral Gold Nanorods.

Circular differential scattering (CDS) spectroscopy has been developed as a powerful method for the characterization of the optical activity of individual plasmonic nanostructures and their complexes with chiral molecules. However, standard measurement setups often result in artifacts that have long raised concerns on the interpretation of spectral data. In fact, the detection limit of CDS setups is constrained by the high level of artifacts, to ±10%. We address this issue by means of a detailed theoretical description of changes in the polarization state when circularly polarized light is reflected at a dark-field condenser. As a result, we propose a modified CDS configuration based on sequentially placing the quarter-wave plate and linear polarizer within the detection optical path, to analyze the circular polarization state of the light scattered by individual particles. Extensive analysis demonstrates a detection limit of ±1.5% for the modified configuration, which is significantly lower than that for the conventional setup. As a standard system for CDS measurements, both achiral and chiral gold nanorods (AuNRs) were characterized using both setups. With achiral AuNRs, linear dichroism (LD) artifacts in the conventional setup are found to originate from LD present in the excitation light and are only present if anisotropic excitation is produced as a result of the misalignment of the excitation light to the condenser. With chiral AuNRs, CDS spectra recorded with the conventional setup depend on the orientation of the chiral AuNRs with respect to the x-axis of the microscope and are reversed compared to those on the colloid and measured in the modified configuration. The results are in good agreement with theoretical simulations for both configurations.

A general design method for ultralong optical path length multipass matrix cells

A general design method for ultralong optical path length multipass matrix cells

Signal quality comparison of customer base and branching methods in fiber to the home network design

One communication medium that is well-known for its outstanding and reliable performance is fiber optic. A social example of its application is the Fiber to the Home (FTTH) network. The goal of this study is to evaluate the signal quality of the customer base method and the branching method, two FTTH-building techniques based on the PT.PLN Icon Plus standards, in order to identify the most practical approach for use in the Air Hitam 2 cluster. Two scenarios were used in this study at the Fiber Access Terminal (FAT) with 1:16 and 1:8 splitters. The fiber optic cable path design findings demonstrate that the branching approach is a wise decision, utilizing optical fiber cables for a total of 9 Km, with the greatest cable distance being 2.5 Km from the Optical Line Terminal (OLT) to the end FAT. According to theory, in the 1:16 splitter situation and the 1:8 splitter scenario, the optical power received by the Optical Network Terminal (ONT) is -19.13 dBm and -16.03 dBm, respectively, with an OLT transmit power of 3 dBm. For these cases, the simulation results are -17.98 dBm and -20.27 dBm. Additionally, the budget value for the rising time reaches 0.253 ns. The bit error rate values in the 1:16 and 1:8 splitter scenarios are 3.157 × 10-10, and 1.63507 × 10-28, respectively, while the Q factor values are 6.18233 and 11.014, respectively. Based on theory and simulation, these findings suggest that the branching strategy can deliver good performance.

Fiber Optic Micro-Hole Salinity Sensor Based on Femtosecond Laser Processing.

This study presents a novel reflective fiber Fabry-Perot (F-P) salinity sensor. The sensor employs a femtosecond laser to fabricate an open liquid cavity, facilitating the unobstructed ingress and egress of the liquid, thereby enabling the direct involvement of the liquid in light transmission. Variations in the refractive index of the liquid induce corresponding changes in the effective refractive index of the optical path, which subsequently influences the output spectrum. The dimensions and quality of the optical fiber are meticulously regulated through a combination of femtosecond laser cutting and chemical polishing, significantly enhancing the mechanical strength and sensitivity of the sensor's overall structure. Experimental results indicate that the sensor achieves salinity sensitivity of 0.288 nm/% within a salinity range of 0% to 25%. Furthermore, the temperature sensitivity is measured at a minimal 0.015 nm/°C, allowing us to neglect temperature effects. The device is characterized by its compact size, straightforward structure, high mechanical robustness, ease of production, and excellent reproducibility. It demonstrates considerable potential for sensing applications in the domains of biomedicine and chemical engineering.

A Trace C2H2 Detection Based on Near‐Infrared Dual‐Comb Spectroscopy

ABSTRACTTo achieve low‐concentration measurement using near‐infrared dual‐comb spectroscopy (DCS), this study presents a trace C2H2 detection using near‐infrared DCS. A multi‐pass gas cell is employed to extend the optical path length, improving the sensor's sensitivity. Signal post‐processing via interpolation method is applied to reduce noise and achieve a flatter dual‐comb. The sensor's sensitivity and transient characteristics are evaluated by selecting absorption lines at 6526.53, 6529.17, and 6531.78 cm−1, with the experimental profile being well‐fitted by a Voigt function. The stability of the system is confirmed with a C2H2 concentration of 200 ppm over a 2.5 h observation period, showing a stability better than 2.305 × 10−2. Allan variance analysis indicates an optimal integration time of 597 s, yielding a minimum detection limit of 6.15 × 10−4 for absorbance and 350 ppb for concentration. Additionally, the detection of nine absorption lines demonstrates the multi‐peak measurement capability, with deviations ranging from 0.059% to 12.496%.

Analysis on thermo-mechanical reliability of laser-electricity converter

Thermal and mechanical responses of a typical Laser-Electricity Converter (LEC) used in laser power beaming to continuous wave (CW) Laser, as well as the damage behavior of key sensor illuminated by laser have been investigated to evaluate the reliability of the converter. Firstly, temperature elevation and thermal stress arising in the whole LEC are calculated and analyzed to find out the vulnerable parts, i.e., the infrared detectors for optical path alignment during wireless power transfer. Then, the parameter dependence of thermo-mechanical behaviors of the detector is revealed with a group of numerical simulations. Finally, the typical experimental tests are carried through to verify the theoretical analysis.

Automatic Optical Path Alignment Method for Optical Biological Microscope.

A high-quality optical path alignment is essential for achieving superior image quality in optical biological microscope (OBM) systems. The traditional automatic alignment methods for OBMs rely heavily on complex masker-detection techniques. This paper introduces an innovative, image-sensor-based optical path alignment approach designed for low-power objective (specifically 4×) automatic OBMs. The proposed method encompasses reference objective (RO) identification and alignment processes. For identification, a model depicting spot movement with objective rotation near the optical axis is developed, elucidating the influence of optical path parameters on spot characteristics. This insight leads to the proposal of an RO identification method utilizing an edge gradient and edge position probability. In the alignment phase, a symmetry-based weight distribution scheme for concentric arcs is introduced. A significant observation is that the received energy stabilizes with improved alignment precision, prompting the design of an advanced alignment evaluation method that surpasses conventional energy-based assessments. The experimental results confirm that the proposed RO identification method can effectively differentiate between 4× and 10× objectives across diverse light intensities and exposure levels, with a significant numerical difference of up to 100. The error-radius ratio of the weighted circular fitting method is maintained below 1.16%, and the fine alignment stage's evaluation curve is notably sharper. Moreover, tests under various imaging conditions in artificially saturated environments indicate that the alignment estimation method, predicated on critical saturation positions, achieves an average error of 0.875 pixels.

Enhancement of Methane Detection in Tunable Diode Laser Absorption Spectroscopy Using Savitzky–Golay Filtering

In order to enhance gas absorption efficiency and improve the detection sensitivity of methane, a gas absorption cell with an effective optical path length of 29.37 m was developed, employing tunable diode laser absorption spectroscopy (TDLAS) and a distributed feedback (DFB) laser with a center wavelength of 1.654 μm as the light source. However, despite these advancements, the detection accuracy was still limited by potential signal interference and noise. To address these challenges, the Savitzky–Golay (S-G) filtering technique was implemented to optimize the TDLAS detection signal. Experimental results indicated a significant enhancement in detection performance. For a methane concentration of 92 ppm, the application of the S-G filter improved the signal-to-noise ratio by a factor of 1.84, resulting in a final device detection accuracy of 0.53 ppm. This improvement demonstrates the effectiveness of the S-G filter in enhancing detection sensitivity, supporting high-precision methane monitoring for atmospheric analysis and various industrial applications.

Research on the Modulation Characteristics of LiNbO3 Crystals Based on the Three-Dimensional Ray Tracing Method

To further study the electro-optical modulation characteristics of LiNbO3 crystals and analyze their modulation performance, a method for studying the modulation characteristics of LiNbO3 crystals, based on the three-dimensional ray tracing method, is introduced. With the help of the refractive index ellipsoidal theory, the optical properties of LiNbO3 crystals under the influence of the Pockels effect are systematically investigated. The research results show that the optical properties of LiNbO3 crystals under the action of an external electric field can be divided into two cases: the crystal optical axis is parallel to the clear light direction, and the crystal optical axis is perpendicular to the clear light direction. Subsequently, starting from Maxwell’s equation and the matter equation, the analytical expressions of optical parameters such as refractive index, wave vector, light vector, optical path, and phase delay in electro-optical crystals are derived. Finally, the propagation law of LiNbO3 crystals when the light is incident in any direction, i.e., when the optical axis of the crystal is parallel to the clear direction and perpendicular to the clear direction, and the light intensity and field of view of the LiNbO3 crystal for electro-optical modulation are discussed.

Coherent characteristics of broadband and extended light sources based on the Twyman–Green interferometer

The Twyman–Green interferometer, as a representative type of interferometric structure, possesses unique advantages in the field of interferometry due to its adjustable single optical path characteristic. However, using a laser as the light source for the Twyman–Green interferometer, with its long coherence length, can result in noisy fringes when measuring planar elements, including multiple surface interference fringes and speckle noise. To address these issues, this paper proposes the use of broadband extended light source as the coherent light source in the Twyman–Green interferometer to achieve short coherent source illumination, thereby eliminating interference fringes and coherent noise. This paper theoretically derives the coherence characteristics of broadband extended light sources and, in particular, quantitatively analyzes the influence of the thickness difference of glass in the Twyman–Green dual optical paths on the contrast of the interference fringe. The corresponding theoretical expressions for interference intensity are derived, and the validity of these theoretical findings is demonstrated through simulation analysis and experimental verification. This innovative research, to our knowledge, significantly supplements the existing coherence theory of light sources, offering substantial theoretical research insights and practical engineering applications.

Raman scattering impairments caused by 50G-PON introduction and mitigation techniques

We explore the impact of stimulated Raman scattering (SRS) in the context of multiple PON generations sharing the same optical distribution network. The 50G-PON, being the last specified ITU-T PON, imposes the use of high launch power to meet strong optical path loss requirements. We show that the XGS-PON upstream could be the first victim of the introduction of 50G-PON since its wavelength spacing maximizes Raman scattering. We exploit a model to describe both in simulation and experiment the SRS-induced depletion on XGS-PON. Assuming that 50G-PON will be deployed on the current passive infrastructure, we also exploit field data to precisely predict the amount of terminations exceeding the requirements. The results show that up to 1.8 dB can be lost on XGS-PON upstream signals, 1.3 dB on the 50G-PON upstream, and 0.5 dB on the G-PON upstream, over a distance of 20 km of fiber. Up to 3% of terminations may be affected, according to our field data exploitation. Improving the receivers’ sensitivity through either better photodiodes, signal processing, or forward error correction could relax the high launch power constraints, and thus the SRS. Deploying an optical splitter at the central office could also limit the power actually launched into the fiber while meeting high split ratios. Finally, decreasing the 50G-PON downstream wavelength seems a possible option to mitigate the Raman scattering.

Symmetric Non-Monochromatic Light as Reference in Fourier Transform Spectrometers.

Fourier transform spectrometers typically use a presumed monochromatic reference source to track and correct errors in optical path difference changes. This paper will conduct a theoretical analysis to show that non-monochromatic light sources with symmetric spectral profiles can also be used as reference sources without adding errors. An experiment was carried out using a symmetric broadband superluminescent diode (SLED) as reference light to measure the spectrum of some other SLED light sources to experimentally demonstrate this finding.

Interferometric Distributed Fiber Optic Vibration Sensor With Branching Sensing Optical Path Based on Time Delay Estimation for Disturbance Localization

Interferometric Distributed Fiber Optic Vibration Sensor With Branching Sensing Optical Path Based on Time Delay Estimation for Disturbance Localization

Three-Dimensional Surface Reconstruction for Specular/Diffuse Composite Surfaces.

This paper presents an effective three-dimensional (3D) surface reconstruction technique aimed at profiling composite surfaces with both specular and diffuse reflectance. Three-dimensional measurements based on fringe projection techniques perform well on diffuse reflective surfaces; however, when the measurement targets contain both specular and diffuse components, the efficiency of fringe projection decreases. To address this issue, the proposed technique integrates digital holography into the fringe projection setup, enabling the simultaneous capture of both specular and diffuse reflected light in the same optical path for full-field surface profilometry. Experimental results demonstrate that this technique effectively detects and accurately reconstructs the 3D profiles of specular and diffuse reflectance, with fringe analysis providing the absolute phase of composite surfaces. The experiments validate the effectiveness of this technique in the 3D surface measurement of integrated circuit carrier boards with chips exhibiting composite surfaces.

Mobile all-light communication network

In reality, both mobile and fixed nodes are required in wireless light communication networks. Dynamic maintenance of light alignment plays a key role in mobile full-duplex light communication. Here, we merge an image identification module and a light communication system on a three-axis gimbal stabilizer. A real-time image of the other light communication system obtained by the image identification module is used as a feedback signal to control the three-axis gimbal stabilizer. Therefore, the other light communication system is automatically tracked, and the optical path between the two light communication ends is dynamically maintained, leading to mobile full-duplex light communication under the transmission control protocol/internet protocol (TCP/IP) scheme. Two green light communication apparatuses are separately deployed on two moving vehicles to establish bidirectional light transmission between moving network nodes with a maximum modulation bandwidth of 4 Mbps. Video communication across air and underwater environments is demonstrated, and internet access is illustrated via a Wi-Fi modem. To overcome environmental barriers, we combine mobile green light communication with blue laser communication, deep-ultraviolet light communication, and 850 nm laser diode communication to develop a mobile all-light communication network that enables seamless connectivity across air, land, and underwater environments. Since this network architecture is based on full-duplex communication, all communication nodes have equal and complete mapping characteristics and can facilitate bidirectional real-time data transmission between arbitrary nodes within the network, offering a promising route toward seamless mobile connectivity using light regardless of the environment.

Multi-Degree-of-Freedom Stretchable Metasurface Terahertz Sensor for Trace Cinnamoylglycine Detection.

Terahertz (THz) spectroscopy, an advanced label-free sensing method, offers significant potential for biomolecular detection and quantitative analysis in biological samples. Although broadband fingerprint enhancement compensates for limitations in detection capability and sensitivity, the complex optical path design in operation restricts its broader adoption. This paper proposes a multi-degree-of-freedom stretchable metasurface that supports magnetic dipole resonance to enhance the broadband THz fingerprint detection of trace analytes. The metasurface substrate and unit cell structures are constructed using polydimethylsiloxane. By adjusting the sensor's geometric dimensions or varying the incident angle within a narrow range, the practical optical path is significantly simplified. Simultaneously, the resonance frequency of the transmission curve is tuned, achieving high sensitivity for effectively detecting cinnamoylglycine. The results demonstrate that the metasurface achieves a high-quality factor of 770.6 and an excellent figure of merit of 777.2, significantly enhancing the THz sensing capability. Consequently, the detection sensitivity for cinnamoylglycine can reach 24.6 µg·cm-2. This study offers critical foundations for applying THz technology to biomedical fields, particularly detecting urinary biomarkers for diseases like gestational diabetes.

Studying the Effect of Transport Layers on ZrS2/MEH-PPV Solar Cells: Using SCAPS -1D Software

This study investigates the effect of charge transport layers on the efficiency of Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH_PPV) and Zirconium Disulfide (ZrS₂) solar cells using Scaps-1D software. It was found that by increasing the MEH-PPV thickness and decreasing its acceptor doping concentration, the efficiency (μ%), fill factor (FF), and short-circuit current density (Jsc ) decreased. Conversely, increasing the thickness of the ZrS₂ electron transport layer and decreasing its donor doping density enhanced the efficiency (μ%) and short-circuit current density (Jsc) while maintaining a constant open-circuit voltage (Voc). These results can be attributed to decreased charge separation and collection in MEH-PPV and reduced optical path length in ZrS2. On the other hand, the back contact with work function is below 4.65 eV, the MEH-PPV/ZrS2 solar cells produced the lowest efficiency compared to different types of back contact. Under optimal conditions, MEH-PPV/ZrS2 solar cell shows a high efficiency of 21% when the dopant concentration of MEH-PPV and the value of the neutral defect density at the ZrS2/ MEH-PPV interface are 1022 cm-3 and 109 cm-3 respectively.