Passive Optical System Research Articles

Multi-Hop GigaBit Ethernet Routing for Gigabit Passive Optical System using Genetic Algorithm

Multi-Hop GigaBit Ethernet Routing for Gigabit Passive Optical System using Genetic Algorithm

Absorption Activity Investigation of Saturable Absorber for Dual Wavelengths in Laser Passive Q-Switching System

Objective: The absorption activity of saturable absorber material (Cr+4: YAG) for dual wavelengths (1.064 μm and 0.946 μm), simultaneously generated in same passive Q-switching system, has been investigated. Methods: This study utilized the mathematical model that was used in our previous study. Rung-Kutta—Fehelberge numerical method has been used to solve this mathematical model. Nd+3: YAG used as an effective medium and Cr+4: YAG used as a saturable absorber in the laser passive Q-switching optical system. Finding: When the population density of saturable absorber increases, the steady state of photons losses occurs at advancement time and the absorption activity reaches to optical bleaching state at advancement time also (it is occurring approximately at time 35 ns from the beginning of the time of pulse construction when the , while at , approximately at time 47 ns). Novelty: The absorption activity of saturable absorber material for a single wavelength of photons oscillating inside the passive Q-switch laser system received attention by some studies. This study verifies or investigates from the behavior of absorption activity of saturable absorber material when encounters photons with two wavelengths oscillating simultaneously inside the laser cavity in order to obtain high power of the pulses. Keywords: Laser, Passive Q­switching, laser, Dual wavelengths laser, Solid state lasers

Movement patterns during gait initiation in older adults with various stages of frailty: a biomechanical analysis

BackgroundGait initiation is challenging for older individuals with poor physical function, particularly for those with frailty. Frailty is a geriatric syndrome associated with increased risk of illness, falls, and functional decline. This study examines whether spatial and temporal parameters of gait initiation differ between groups of older adults with different levels of frailty, and whether fear of falling, and balance ability are correlated with the height of lifting the food during gait initiation.MethodsSixty-one individuals aged > 65 years, classified by Fried frailty phenotype, performed five self-paced gait initiation trials. Data was collected using a three-dimensional passive optical motion capture system, consisting of 10 cameras with the ability to perceive reflective markers, and two force plates. The total duration of gait initiation and the duration of its four sub-phases, the first step length, and the maximum foot clearance during the first step were derived, and compared statistically between groups. Additionally, an association analysis was conducted between foot clearance and fear of falling, and confidence in balance in older individuals.ResultsFrail individuals had significantly longer unloading durations, and total durations of gait initiation compared to non-frail older adults. Additionally, they had shorter first step lengths compared to non-frail older adults. Pre-frail older adults also showed shorter steps compared to the non-frail group. However, there were no significant differences between groups for the maximum foot clearance during the first step. Nevertheless, the maximum foot clearance of older individuals correlated significantly with their fear of falling and confidence in balance.ConclusionOlder adults with reduced physical function and signs of frailty mainly display longer duration of gait initiation and decreased first step length compared to non-frail older adults. The release phase is decreased as the double support phase is prolonged in frail patients. This information can guide the development of specialized exercise programs to improve mobility in this challenging motion between static and dynamic balance.

Design and Research of Laser Power Converter (LPC) for Passive Optical Fiber Audio Transmission System Terminal

In environments like coal mines and oil wells, electrical equipment carries the risk of disasters such as underground fires and methane gas explosions. However, communication equipment is essential for work. Our team has developed a long-range (approximately 25 km) audio transmission system that operates without the need for terminal power sources, thereby eliminating the risk of electrical sparks. This system leverages the reliability of optical fiber and employs a 1550 nm laser for analog audio transmission. After traveling through 25 km of optical fiber, the signal is converted back into electrical energy using a custom-designed Laser Power Converter (LPC). The optical fiber’s carrying capacity imposes limits on the light signal intensity, which, in turn, affects the signal transmission distance. To enable long-distance transmission, we have carefully chosen the optical wavelength with minimal loss. We observed that different LPC structures operating within the same wavelength band have an impact on the audio quality at the terminal. By comparing their characteristics, we have identified the key factors influencing audio output. The optimal LPC allows audio transmission over 25 km, with an output exceeding 12 mVrms.

Improved passive optical network RoF system based vertical cavity-surface emitting laser (VCSEL) optical source external modulation

Passive Optical Network (PON) is a promising 5 G optical fiber network technology, that can enhance reliability data rate, and bandwidth saving. This simulation-based study investigates the feasibility of implementing a vertical cavity-surface emitting laser (VCSEL) optical source along with wavelength-division multiplexing (WDM) for designing a PON radio over fiber (RoF) system that can authorize multi-subscribers, users, to simultaneously use the same optical fiber for Front long-haul data transmission. Three scenarios are proposed: First, a VCSEL, and a Mach–Zehnder Modulator with a distinctive frequency are made accessible to every user in the PON system. Whereas, in the second scenario, a continuous wave (CW) laser is used to replace the VCSEL in the same PON. 16 users are multiplexed by a WDM and transmitted over a link length of 200 km. The system performance is, thus measured in terms of Q-factor, and it is revealed that the VCSEL-based system outperforms the system utilized CW laser to a distance of 150 km, with a maximum gain in the Q-factor of about 4.5. Both postulated systems are able to achieve a maximum transmission distance of 180 km with a minimum Q-factor of 6. Moreover, to minimize, the input current of around 1 mA and the system complexity, a third scenario is presented in which one VCSEL with 193.1 THz is shared among multiple users. The Q-factor performance is then simulated for up to 72 users, revealing that the minimum level of acceptable Q-factor has been maintained up to a link length of 180 km.

Dynamics of solitons in Lugiato–Lefever cavities with fractional diffraction

We study soliton dynamics in a passive optical system governed by the Lugiato–Lefever equation with effective diffraction represented by a fractional spatial derivative. Two models are considered, with the spatially uniform or strongly localized pump. Stable (quasi-) solitons are constructed, and their stability regions in the systems’ parameter spaced are identified primarily, in a numerical form. The stability is strongly affected by the Lévy index (LI) of the fractional diffraction. The dependence of the stability on the loss coefficient and pump strength, as well as the localization size in the case of the confined pump, are studied too. In the latter case, the stability is enhanced by the narrow localization. Unstable solitons spontaneously develop intrinsic oscillations. In the case of the localized pump, some unstable solitons escape from the position pinned to the pumped region.

Design of long-distance multichannel system based on passive optical fiber audio transmission system

To meet sound transmission requirements in complex work environments, this paper constructs a passive audio pickup sensor based on an extrinsic Fabry-Perot interferometer (EFPI) and develops a one-way four-channel passive audio parallel transmission system based on a passive bidirectional audio over fiber(PB-AOF) transmission system and wavelength division multiplexing technology. The system realizes optical fiber audio transmission over a distance of 20 km. The experimental results show that the signal-to-noise ratio (SNR) is greater than 64 dB, and the highest sensitivity of the four channels in the proposed system is 1.06 V/Pa. Thus, the proposed long-distance terminal passive audio communication network is ideally suited for applications in certain fields.

Photonic reservoir computing enabled by stimulated Brillouin scattering.

Artificial intelligence (AI) drives the creation of future technologies that disrupt the way humans live and work, creating new solutions that change the way we approach tasks and activities, but it requires a lot of data processing, large amounts of data transfer, and computing speed. It has led to a growing interest of research in developing a new type of computing platform which is inspired by the architecture of the brain specifically those that exploit the benefits offered by photonic technologies, fast, low-power, and larger bandwidth. Here, a new computing platform based on the photonic reservoir computing architecture exploiting the non-linear wave-optical dynamics of the stimulated Brillouin scattering is reported. The kernel of the new photonic reservoir computing system is constructed of an entirely passive optical system. Moreover, it is readily suited for use in conjunction with high performance optical multiplexing techniques to enable real-time artificial intelligence. Here, a methodology to optimise the operational condition of the new photonic reservoir computing is described which is found to be strongly dependent on the dynamics of the stimulated Brillouin scattering system. The new architecture described here offers a new way of realising AI-hardware which highlight the application of photonics for AI.

Real-time wavefront correction using diffractive optical networks.

Real-time wavefront correction is a challenging problem to present for conventional adaptive optics systems. Here, we present an all-optical system to realize real-time wavefront correction. Using deep learning, the system, which contains only multiple transmissive diffractive layers, is trained to realize high-quality imaging for unknown, random, distorted wavefronts. Once physically fabricated, this passive optical system is physically positioned between the imaging lens and the image plane to all-optically correct unknown, new wavefronts whose wavefront errors are within the training range. Simulated experiments showed that the system designed for the on-axis field of view increases the average imaging Strehl Ratio from 0.32 to 0.94, and the other system intended for multiple fields of view increases the resolvable probability of binary stars from 30.5% to 69.5%. Results suggested that DAOS performed well when performing wavefront correction at the speed of light. The solution of real-time wavefront correction can be applied to other wavelengths and has great application potential in astronomical observation, laser communication, and other fields.

A PON Monitoring System Integrating Fault Detection and Localization

We propose and experimentally demonstrate an integrated passive optical network monitoring system for fault detection and localization. Fault detection technology is based on the recognition of reflection spectrum generated by each single fiber Bragg grating, which can support large-capacity user fiber fault monitoring. Fault localization method uses two different total received powers measured by an optical power meter to solve the established equation, and it shows a good accuracy compared with the OTDR measurement results. Fault detection and localization are carried out separately but share the same transmitter module. The introduction of the additional module ensures that the troubleshooting does not affect other normal user data communication. We also investigate the dynamic range requirements of the fault detection technology and the measurement error of the fault localization method. The calculation results show the required dynamic range for the recognition device can be maintained within a small range and the use of high-accuracy optical power meter can reduce the measurement error. The proposed monitoring system can simultaneously provide a large-capacity fault detection technology and high-accuracy fault localization method in a cost-sensitive passive optical network market.

Evaluation and Comparison of Target Registration Error in Active and Passive Optical Tracking Systems.

Optical tracking systems combined with imaging modalities such as computed tomography and magnetic reso-nance imaging are important parts of image guided surgery systems. By determining the location and orientation of sur-gical tools relative to a patient's reference system, tracking systems assist surgeons during the planning and execution of image guided procedures. Therefore, knowledge of the tracking system-induced error is of great importance. To this end, this study compared one passive and two active optical tracking systems in terms of their Target Registration Error. Two experiments were performed to measure the systems' accuracy, testing the impact of factors such as the size of the measuring volume, length of surgical instruments and environmental conditions with orthopedic procedures in mind. According to the performed experiments, the active systems achieved significantly higher accuracy than the tested passive system, reporting an overall accuracy of 0.063 mm (SD = 0.025) and 0.259 mm (SD = 0.152), respectively.

Performance enhancement of hybrid fiber wavelength division multiplexing passive optical network FSO systems using M-ary DPPM techniques under interchannel crosstalk and atmospheric turbulence

The performance of moment generating function approaches, specifically Chernoff bound (CB) and modified Chernoff bound (MCB), is examined and improved in this study. We evaluates and enhances the performance of a wavelength division multiplexing (WDM) technique for free-space optical (FSO) fibre communications based on passive optical network (PON) using the M-ary digital pulse-position modulation (M-ary DPPM) schemes under amplified spontaneous emission (ASE) noise effects, interchannel crosstalk (ICC), and atmospheric turbulence (AT). We use a data rate of 2.5 Gbps for eight channels over a PON/DWDM-FSO optical fibre system in the C-band with 100 GHz channel spacing start from 1550 nm. The results achieve 20 Gbit/s transmissions (2.5 Gbps $$\times $$ 8 channels). This is a technology that can have extended leverage, higher data rates, power-efficient, and is considered an ideal option for the provision of bandwidth for potential access networks. When compared to the CB at a low gain (G = 8), the MCB outperforms the Gaussian approximation at high gain (G = 30). Because of its superior performance at a high gain (G = 30), the MCB offers the tightest limit on the bit error rate (BER). In comparison to an equivalent on–off keying (OOK) non-return-to-zero (NRZ), the M-ary DPPM scheme with a coding level (M) of 2 improves average power about by 2.9 dB at a data rate of 2.5 Gbps on the 1550 nm wavelength and BER of $${10}^{-{9}}$$ . The sensitivity of the M-ary DPPM modulation scheme remains improved over OOK in the presence of ICC. The lower power penalty is predicted to be approximately 0.2–3.0 dB in the DWDM-FSO systems for low coding level M $$=$$ 2. We achieve a lower power penalty at 0.2–3.0 dB for the hybrid fiber DWDM/PON-FSO optical communication system at a BER of $${10}^{-{9}}$$ . At a target BER of $${10}^{-{12}}$$ , the hybrid OOK-NRZ/M-ary DPPM offers about 4–8 dB of optical signal-to-noise-ratio improvements over the M-DPPM of the WDM-PON/FSO link for strong turbulence. The results demonstrated that the M-ary DPPM and the optical relaying amplification technique are powerful treatments for mitigating the impacts of ASE noise, AT, and ICC.

Study on Automatic Tracking Method of Marking Points in Sports Image Sequence

Background: The effect of teaching and training in physical sports is improved by the sports demonstration system. The two-dimensional sports demonstration system is widely applied for the training of athletes. In accurate motion positioning, there exists a certain visual deficiency and the two-dimensional sports demonstration system is analyzed by kinematics. Methodology: Aiming at the problems in the real-time tracking of fast-moving targets in sports images, an automatic tracking method of sports images based on the registration of landmark points of the passive optical motion capture system is proposed. Moreover, it aims to build a human model and divide the human model into several limb segments; find the corresponding relationship between the first frame of motion data and template data to complete the first frame of motion data registration; based on the smallest non-rigid deformation and point set matching error, find the corresponding relationship between the current frame of motion data and the previous frame of registered motion data; through the mark points, follow up to complete the registration process of the marker. Results: Experiments show that the average processing accuracy of this algorithm can reach over 85% and the processing time of a single frame of motion data is t<1/60s, which can meet real-time requirements. Conclusion: The multi-point set least-squares matching algorithm is used to rigidly correct the registered landmark data. No manual intervention is required for the entire mark registration process.

Optimal efficiency for passively coupling partially coherent light into mode-limited optical waveguides

In this paper, we examine the problem of coupling partially coherent light from a telescope into an optical fiber within the framework of phase space optics using Wigner distributions. Specifically, we consider optimization of the coupling efficiency for passive optical systems under constraints in the number of spatial modes guided by the optical fiber, as are often imposed by the limitations of fiber devices or detectors employed later in the optical chain. As our primary example, we consider in detail the case of monochromatic plane wave optical fields distorted by random phase perturbations caused by propagation through atmospheric turbulence. By analyzing the Wigner distribution function for a plane wave in atmospheric turbulence, we develop an expression for the coupling efficiency as a function of the number of fiber modes and the ratio of the telescope diameter to Fried’s atmospheric coherence diameter.

Giant and tunable Goos-Hänchen shift with a high reflectance induced by PT-symmetry in atomic vapor.

The Goos-Hänchen (GH) shifts of light beams reflected from conventional passive optical systems could be enhanced using the Brewster angle effect or resonance effect, but the maximum GH shift is located at the reflectance minima, which is difficult for experimental detection. In this paper, we present an efficient and flexible scheme to realize complex parity-time (PT)-symmetric periodic optical potentials (complex crystals) in helium atomic vapor. The GH shifts of probe light reflected from the complex crystal are theoretically investigated and large GH shifts could be obtained inside the high-reflection band. When the complex crystal is operated near the coherent perfect absorption-laser point, the maximum GH shift of probe light is exactly located at the reflectance peak. Moreover, the GH shifts could be easily controlled by adjusting the intensity of control light.

The stare and chase observation strategy at the Swiss Optical Ground Station and Geodynamics Observatory Zimmerwald: From concept to implementation

A sustainable use of the outer space becomes imperative for preserving current operational missions and enabling the placement of new space-based technology in the outer space safely. The uncontrolled growing number of resident space objects (RSO) increases the likelihood of close conjunctions and therefore collisions that will populate the space environment even more. To prevent such situations, orbit catalogues of RSO are built and maintained, which are used to assess the collision risk between RSO. In order to keep the catalogues up-to-date, a worldwide ground-based infrastructure is used to collect observations coming from different observation techniques.The current study focuses on the so-called stare and chase observation strategy using an active and passive-optical system. The final aim is to correct the pointing of the telescope so that the target will be within the field of view of the laser beam, thus enabling the acquisition of laser ranges. By doing so, objects with poor ephemerides, available e.g. from Two Line Elements (TLE), will not pose a problem anymore for the rather small field of view of the laser beam. The system gathers both angular and range measurements, which can be used for an immediate orbit determination, or improvement, that will enhance the accuracy of the predictions helping other stations to acquire the target faster and permitting the station to repeat the procedure once more.The development of the observation strategy is particularized for the Zimmerwald Laser and Astrometry Telescope (ZIMLAT), located at the Swiss Optical Ground Station and Geodynamics Observatory Zimmerwald (SwissOGS), Switzerland. Likewise, all the implemented algorithms were tested using real measurements from ZIMLAT and the tracking camera.

Ultralow‐Loss Etchless Lithium Niobate Integrated Photonics at Near‐Visible Wavelengths

AbstractLithium niobate is considered as the “silicon of photonics” because of its many excellent optical properties as well as a wide transparency window covering the visible to mid‐infrared wavelength range. Here, by using the principle of bound states in the continuum, lithium niobate integrated photonics at near‐visible wavelengths with an etchless fabrication process is developed, which achieves a minimal propagation loss of 1.8 dB cm−1 in straight waveguides at the wavelength of ≈771 nm and a maximal intrinsic Q factor of 1.1 × 106 in disk microcavities at ≈765 nm. Typical integrated photonic components including Mach–Zehnder interferometers and multimode directional couplers are also demonstrated. Based on the experimental results, a convenient scheme of second‐harmonic generation is proposed for converting light in the fundamental TE‐polarized mode at a telecom wavelength into the second‐order TM‐polarized mode at a near‐visible wavelength. The demonstrated etchless lithium niobate integrated photonic platform can support both passive and active optical devices and systems on a chip for various visible‐light applications including optical imaging, nonlinear optics, and quantum information processing.

Optical Inspection Systems for Axisymmetric Parts with Spatial 2D Resolution

The article proposes a solution to the problem of increasing the accuracy of determining the main shaping dimensions of axisymmetric parts through a control system that implements the optical method of spatial resolution. The influence of the projection error of a passive optical system for controlling the geometric parameters of bodies of revolution from the image of its sections, obtained by a digital camera with non-telecentric optics, on the measurement accuracy is shown. Analytical dependencies are derived that describe the features of the transmission of measuring information of a system with non-telecentric optics in order to estimate the projection error. On the basis of the obtained dependences, a method for compensating the projection error of the systems for controlling the geometry of the main shaping surfaces of bodies of revolution has been developed, which makes it possible to increase the accuracy of determining dimensions when using digital cameras with a resolution of 5 megapixels or more, equipped with short-focus lenses. The possibility of implementing the proposed technique is confirmed by the results of experimental studies.

APPARILLO: a fully operational and autonomous staring system for LEO debris detection

For safe operation of active space crafts, the space debris population needs to be continuously scanned, to avoid collisions of active satellites with space debris. Especially the low Earth orbit (LEO) shows higher risks of collisions due to the highest density of orbital debris. Laser ranging stations can deliver highly accurate distance measurements of debris objects allowing precise orbit determination and more effective collision avoidance. However, a laser ranging station needs accurate a priori orbit information to track an orbital object. To detect and track unknown orbital objects in LEO, here, a passive optical staring system is developed for autonomous 24/7 operation. The system is weather-sealed and does not require any service to perform observations. To detect objects, a wide-angle imaging system with 10° field of view equipped with an astronomical CCD camera was designed and set up to continuously observe the sky for LEO objects. The system can monitor and process several passing objects simultaneously without limitations. It automatically starts an observation, processes the images and saves the 2D angular measurements of each object as equatorial coordinates in the TDM standard. This allows subsequent initial orbit determination and handover to a laser tracking system. During campaigns at twilight the system detected up to 36 objects per hour, with high detection efficiencies of LEO objects larger than 1 m3. It is shown that objects as small as 0.1 m3 can be detected and that the estimated precision of the measurements is about 0.05° or 7 × the pixel scale.

Dynamic Joint Motions in Occupational Environments as Indicators of Potential Musculoskeletal Injury Risk.

The objective of this study was to test the feasibility of using a pair of wearable inertial measurement unit (IMU) sensors to accurately capture dynamic joint motion data during simulated occupational conditions. Eleven subjects (5 males and 6 females) performed repetitive neck, low-back, and shoulder motions simulating low- and high-difficulty occupational tasks in a laboratory setting. Kinematics for each of the 3 joints were measured via IMU sensors in addition to a "gold standard" passive marker optical motion capture system. The IMU accuracy was benchmarked relative to the optical motion capture system, and IMU sensitivity to low- and high-difficulty tasks was evaluated. The accuracy of the IMU sensors was found to be very good on average, but significant positional drift was observed in some trials. In addition, IMU measurements were shown to be sensitive to differences in task difficulty in all 3 joints (P < .05). These results demonstrate the feasibility for using wearable IMU sensors to capture kinematic exposures as potential indicators of occupational injury risk. Velocities and accelerations demonstrate the most potential for developing risk metrics since they are sensitive to task difficulty and less sensitive to drift than rotational position measurements.