Beam Divergence Angle Research Articles

Investigation and demonstration of a high-power handling and large-range steering optical phased array chip

The optical power handling of an OPA scanning beam determines its targeted detection distance. So far, a limited number of investigations have been conducted on the restriction of the beam power. To the best of our knowledge, we for the first time in this paper explore the ability of the silicon photonics based OPA circuit for the high power application. A 64-channel SiN-Si based one-dimensional (1D) OPA chip has been designed to handle high beam power to achieve large scanning range. The chip was fabricated on the standard silicon photonics platform. The main lobe power of our chip can reach 720 mW and its peak side-lobe level (PSLL) is -10.33 dB. We obtain a wide scanning range of 110° in the horizontal direction at 1550 nm wavelength, with a compressed longitudinal divergence angle of each scanning beam of 0.02°.

Single-scatter path loss model of LED-based non-line-of-sight ultraviolet communications.

Light-emitting diodes (LEDs) are popularly used as light sources in non-line-of-sight (NLOS) ultraviolet communications (UVC). However, currently reported single-scatter path loss (PL) models of NLOS UVC links assume that the radiant intensity of the light source is uniformly distributed within the beam divergence angle, which cannot well characterize the light emission pattern of LEDs. In this Letter, we propose a single-scatter PL model for LED-based NLOS UVC systems, and the corresponding analytical expression is derived by modeling the LED emission pattern as a Lambertian distribution. Monte Carlo simulations and experimental results are provided to verify the effectiveness of the proposed PL model. Results show that the proposed model can accurately predict PL results in actual situations. The root-mean-square error of the proposed PL model is only about 1 dB in typical scenarios with experimental results as benchmarks. Also, the proposed model is much easier to implement than the currently reported PL model with the light source model of a uniformly distributed emission pattern.

Research on the method of designing cap lens using ant colony algorithm

It is necessary to select the appropriate parameters defining a aspheric lens for coupling the light from a laser diode into the optical fiber by cap aspheric lenses. In this paper, the ant colony optimization algorithm is applied to the optimization of structural parameters of the cap aspheric lens, and the merit function defining the optimization problem and detailed design steps are given. A cap aspheric lens with center thickness of 1.1019 mm and effective focal length of 1.10331 mm is designed using a self-made MATLAB program of ant colony optimization algorithm, which can couple the light emitting from a laser diode into a single mode fiber with a diameter of 9 um, the light-emitting surface of the LD is 3 µm × 2 µm, and beam-divergence angle in the X and Y directions are ± 35° and ± 23.58°, respectively. The theoretical coupling efficiency is 89.8%, and the experiment shows that the maximum coupling efficiency and average coupling efficiency are 88.63% and 79.39%, respectively. Design and experimental results prove that the design method in this paper is feasible and effective.

Design and alignment of off‐axis reflection beam expanding and contracting optical system

AbstractThere are special requirements for the laser beam diameter and divergence angle in various optical combination systems, so most of the designs add beam expansion and contraction systems. Off‐axis reflective systems are more widely used in practical applications because of their nonobstructing characteristics and unaffected by chromatic aberration. This paper designs an optical system with both beam expansion and contraction functions by Zemax optical software according to actual needs. The magnification and reduction are 3×. The mirror surface adopts an aspheric design to overcome system aberrations. The off‐axis reflective structure is suitable for lasers of different wavelengths (632.8 nm, 1064 nm, and 1550 nm) without being affected by chromatic aberration. The optical spot diagram shows that the light spot distribution is uniform and meets the magnification and reduction ratio. Besides, combined the dynamic laser interferometer, we install and debug the primary and secondary mirrors of the system and use the laser beam quality analyzer to measure the exit spot of the actual laser beam after passing through the designed optical system. The peak value and root‐mean‐square value of the system transmission wave front are less than 0.1λ. The beam quality test result of the outgoing spot meets the actual application requirements and image quality requirements.

Correct measurement methodology spatial-energy characteristics of laser beams

A methodology for correct measurements of the spatial and energy characteristics of a laser beam is considered, based on the determination of the initial moments of the spatial intensity distribution in the beam cross section. The classification of radiation fields participating in the measuring process is given: emitted, measured and measured. It is shown that ISO 11146:2005 “Lasers and laser-related equipment. Test methods for laser beam widths, divergence angles and beam propagation ratios, Part 1-3” for measuring the spatial and energy characteristics of laser beams leads to incorrect measurements. This is due to the fact that the recommendations for the application of ISO 11146:2005 do not take into account the dynamic range of the used matrix radiation detectors, and the characteristics of the emitted field of interest to the user turn out to be diverging, which violates the uniformity of measurements. Moreover, the conditions ensuring the convergence of the results are practically impracticable. To solve these problems, it is proposed to establish and regulate the lower level of the dynamic range of measurements of the intensity of the used matrix receivers and to consider the spatial and energy characteristics of the emitted field of interest to the user, depending on the set value of the lower level. It is shown that measurements with this methodology become correct and make it possible to compare the characteristics of laser beams obtained by different array detectors. Formulas are given that take into account the effect of the lower level of the dynamic range of the matrix radiation detectors on the measurement result. These formulas should be recommended for inclusion in the updated edition of the national standard GOST R ISO 11146-2008 “Lasers and laser installations (systems). Methods for measuring widths, divergence angles and propagation coefficients of laser beams. Parts 1-3”.

Numerical and theoretical modeling of the sheath upstream of ion optics: sheath structure transition and its effect on the beam divergence

The grasp of the sheath characteristics is fundamental to evaluate the extraction capabilities of ion optics and accommodate the wide application of ion sources. A one-dimensional theoretical model is developed to investigate the sheath upstream of ion optics as well as the matching relation between the ion optics and plasma, by simplifying and decomposing the Poisson’s equation at the outer surface and centerline of the grid aperture. The one-dimensional model is validated by 2D3V hybrid simulations which are also applied to visualize the sheath structure and ion beam divergence. With the increase of plasma density, it is found that the upstream sheath will transform gradually into a sheath near the plate electrode at first and then enter the screen aperture with a sheath edge approximately paralleling to the meniscus. Accordingly, the structure of the upstream sheath can be classified into four kinds which correspond to different beam divergence. The structure transition of the upstream sheath reflects the interaction between the extraction field and plasma, and the ion optics is considered to work at the matching point when the plasma is relatively balanced with the extraction field. Around the matching point, a small beam divergence angle can be achieved without the occurrence of over-perveance. Then a matching model is proposed based on the characteristics of the potential distribution at the matching point. It is verified to be effective of the model for quickly analyzing the ion beam divergence characteristics and determining an ideal operating range of the ion optics.

Study on Satellite-to-ground Laser Communications with Existence of Atmosphere<sup>*</sup>

The laser beam used to establish a communication channel between satellite and ground segments has a small divergence angle and a tiny spot on the Earths surface, which may lead to the fail of the system. So its important to study the deflection of laser beam by the Earths atmosphere and find a way to calibrate this error. Both theoretical analysis and real data processing method are used to obtain the mathematical model for divergence angle of laser communication beam and its correction function. Then the model has been applied to the data, which was used to describe the atmosphere state by traditional ground segments to obtain the critical elevation angle. According to the results of calculation, our conclusion will be that the correction should be done when the critical elevation happens.

Performance analysis of coherent free‐space optics transmission link using in‐phase quadrature modulator‐based polarization multiplexed‐256‐quadrature amplitude modulation

AbstractA single‐channel high information rate free‐space optics transmission link is presented incorporating in‐phase quadrature modulator‐based polarization multiplexed‐256‐quadarature amplitude modulation scheme. An information rate of 160 Gbit/s with 10 Gbaud symbol rate is achieved for free‐space information transmission. Advanced digital signal processing techniques at the receiver along coherent detection have been used to compensate the losses incurred by the information signal propagating the free‐space media. The transmission performance of the proposed link has been enhanced by using different optical amplifiers, that is, Erbium‐doped fiber amplifier and semiconductor optical amplifier, and their performance has been compared. The link performance is analyzed for required laser line width, launch power requirements, increasing transmission range, increasing beam divergence angle and optical power required at the receiver. Bit error rate and error vector magnitude metrics have been used to analyze the link performance. A maximum transmission of 3.9 km for clear weather atmospheric conditions is achieved. The proposed link has the potential to meet the last‐mile access needs and to provide high‐bandwidth high‐speed information links required for future fifth generation wireless communication and Internet of Things applications.

Simplified Closed-Form Single-Scatter Path Loss Model of Non-Line-of-Sight Ultraviolet Communications in Noncoplanar Geometry

Considering the wide acceptability and practicability of single-scatter path loss (PL) model of non-line-of-sight (NLOS) ultraviolet communications (UVC) in noncoplanar geometry and the corresponding complexity of the triple integrals in the exact single-scatter PL model, a novel simplified PL model is proposed in this work with better analytical tractability and high accuracy. By approximately regarding the differential volume as a circular and thin plate, the triple integrals in the exact single-scatter PL model can be reduced to a single integral. With different baseline ranges between transmitter and receiver, beam divergence angles, receiver field-of-view (FOV) angles, inclination angles and azimuth angles taken into account, the results of the proposed PL model are compared with those of an exact single-scatter PL model, a Monte Carlo numerical model, and another recently reported approximate single-scatter PL model, which is called spherical crown (SC) model. Compared with the SC model, the proposed single-scatter PL model is obtained in closed form. Besides, taking the exact single-scatter PL model as the benchmark, the root-mean-square error (RMSE) of the proposed model and the SC model are calculated for comparison. It is demonstrated that the proposed model could achieve better accuracy than SC model under most conditions of our interest. Besides, it is shown that the RMSE of the proposed model is less than 0.4 dB for all considered transceiver geometry and the execution time of the proposed PL model is significantly reduced to less than 1% of the exact single-scatter PL model’s, which manifests the effectiveness of the proposed model. Finally, the experimental results are also provided to verify the correctness of the proposed model.

Flow visualization and density measurement of the supersonic molecular beam for fusion plasma fueling.

The supersonic molecular beam injection (SMBI) technique is widely used in magnetic fusion devices for plasma fueling and active control of particles. The beam flow formed by the SMBI system is directly visualized by a newly established schlieren diagnostic system on the SMBI testing platform. This schlieren system could provide a 2D density distribution of the beam with the sub-mm spatial resolution by detecting the change in the refractive index of the medium caused by the SMBI in the low-pressure vacuum chamber. The structure and the divergence angle of the supersonic molecular beam for fusion plasma fueling are first measured. Additionally, the density profile of the supersonic molecular beam is reconstructed from the measured light intensity by the schlieren system. The experimental comparison between the standard nozzle and the optimized nozzle of the SMBI system shows the great potential of the diagnostic system in optimizing the beam characteristics.

Propagation of a Modified Complex Lorentz–Gaussian-Correlated Beam in a Marine Atmosphere

In this paper, we study the second-order statistics of a modified complex Lorentz–Gaussian-correlated (MCLGC) beam, which is a new type of partially coherent beam capable of producing an Airy-like intensity pattern in the far field, propagation through marine atmospheric turbulence. The propagation formula of spectral density is derived by the extended Huygens–Fresnel integral, which could explicitly indicate the interaction of turbulence on the beams’ spectral density under propagation. The influences of the structure constant of the turbulence, initial coherence width and wavelength on the spectral density are investigated in detail through numerical examples. In addition, analytical expressions for the r.m.s beam width, divergence angle and M2 factor of the MCLGC beam in the marine turbulence are also derived with the help of the Wigner distribution function. The results reveal that the beam spreads much faster, and the M2 factor deteriorates severely with the increase of the structure constant and the decrease of the inner scale size, whereas the outer scale size has little effect on these two quantities.

Research on the performance of SIMO RC-OFDM system with exponential Weibull distribution in the downlink satellite–terrestrial laser communication

In this paper, a repetition code (RC) coherent orthogonal frequency division multiplexing (OFDM) single input multiple output (SIMO) system based on the exponential Weibull distribution model is proposed for downlink satellite–terrestrial laser communication. The closed form expression of bit error rate (BER) of the SIMO RC-OFDM system is derived by considering the joint effect of downlink intensity scintillation and angle of arrival fluctuation (AOA). The relationship between the BER and signal-to-noise ratio (SNR) of uncoded system and SIMO RC-OFDM system is compared under weak, medium and strong atmosphere turbulence, and the influence of the number of receiver antennas on the SIMO RC-OFDM system is studied. At the same time, under the condition of weak turbulence, the influence of important indicators such as zenith angle, receiving aperture, optimal beam divergence angle, and optimal transmission radius on the satellite–terrestrial laser communication downlink SIMO RC-OFDM system is analyzed. The Monte Carlo (MC) principle uses randomness to solve integral problems, and the obtained results are verified by MC simulations. This work provides a theoretical basis for research on coding technology in satellite–terrestrial laser downlink communication SIMO systems.

Investigation on a 220 GHz Quasi-Optical Antenna for Wireless Power Transmission

This paper investigates a 220 GHz quasi-optical antenna for millimeter-wave wireless power transmission. The quasi-optical antenna consists of an offset dual reflector, and fed by a Gaussian beam that is based on the output characteristics of a high-power millimeter-wave radiation source-gyrotron. The design parameter is carried on by a numerical code based on geometric optics and vector diffraction theory. To realize long-distance wireless energy transmission, the divergence angle of the output beam must be reduced. Electromagnetic simulation results show that the divergence angle of the output beam of the 5.6 mm Gaussian feed source has been significantly reduced by the designed quasi-optical antenna. The far-field divergence angle of the quasi-optical antenna in the E plane and H plane is 1.0596° and 1.0639°, respectively. The Gaussian scalar purity in the farthest observation field (x = 1000 m) is 99.86%. Thus, the quasi-optical antenna can transmit a Gaussian beam over long-distance and could be used for millimeter-wave wireless power transmission.

Değişik Ortam Ve Sistem Parametreleri İçin Sualtı Kablosuz Optik Haberleşme Monte Carlo Kanal Kapasitesinin İncelenmesi

Increasing interest in oceans increases the scientific, commercial and military studies in this field, in which underwater wireless communication systems are frequently used. In literature, underwater wireless, synchronous, high speed data transfer can only be done with optical systems. The distorting effects of underwater environment (UE) on optical waves significantly affect the communication distance and speed of underwater wireless optical communication (UWOC) systems. Therefore, in order to design reliable UWOC systems, it is important to examine effects of various UEs on UWOC systems on a realistic channel model. In this study, instead of the approximate channel models, Monte Carlo approach UWOC channel model, which is accepted in literature with its high accuracy and sensitivity, was used, and effects of the transmitter's beam divergence angle and aperture diameter of receiver parameters, which are important design parameters for UWOC systems, on a typical UWOC system were investigated. In this study, three various UEs, namely clean ocean, coastal ocean and harbor waters, which are frequently used as benchmarks in the literature, were taken into consideration, and channel impulse responses, signal to noise ratios and channel capacity distributions were presented and interpreted for each UE. With the results obtained, the communication speed and distance limits of a typical UWOC system were determined, and a prediction was provided for UWOC systems that can be used in various UEs and parameter values.

Performance analysis of MRR FSO communication system under Gamma–Gamma​ turbulence channel with pointing error

The performance of modulating retro-reflector (MRR) free space optical (FSO) communication system has been studied before for various atmospheric turbulence conditions. However, the effect of pointing error (PE) on the MRR FSO communication system has not been studied yet. In this work, we investigate the PE impact on the MRR FSO communication system. Specifically, we obtain the probability density function (PDF) of the system in closed form expression regarding Gamma–Gamma turbulence channel and Rayleigh PE. Using this PDF, we derive the statistical characteristics closed form expressions of the received optical signal-to-noise ratio (SNR) including PDF, cumulative distribution function (CDF), moments and moment generating function (MGF). Relying on the obtained analytical results, we derive the system average bit error rate (BER), outage probability, ergodic capacity (EC) and amount of fading (AF) performances in closed forms. The closed form expressions are given in terms of Meijer’s G-function with the exception of obtaining the moments of the received optical SNR and AF in terms of elementary functions. For the given weather, PE and system conditions, we optimize the beam divergence angle to minimize the system average BER. Based on this, we suggest controlling of the beam divergence angle with the transmission distance according to the optimum beam divergence angle to improve the system BER performance. Finally we demonstrate the system performances according to the optimum beam divergence angle.

Realization of Multimode OAM Beams with Almost the Same Divergence Angles

This paper proposes a new method of realizing multimode OAM beams with almost the same divergence angles. The theoretical relationship between the divergence angle of the OAM beam and its radiation source is presented, and the radiation source distributions for various mode OAM beams with the same divergence angle range are discussed. In order to verify this method, an eight-mode OAM antenna constructed by a bifocal parabolic reflector and dual OAM feeds is designed and simulated. The simulation results show that the divergence angle ranges of 3 dB beamwidth for OAM modesl=±1,±2,±3,±4are2.2°,4.6°,2.2°,5.0°,2.4°,4.4°, and 2.6°,4.8°, the divergence angles corresponding to the maximum beam directions are3.5°,3.6°,3.5°, and 3.8°, respectively, and the maximum difference is within0.3°.

Development of megawatt radiofrequency ion source for the neutral beam injector on HL-2A tokamak

A radiofrequency (RF) ion source with a megawatt power extraction, thunder I, has been developed for the neutral beam injector (NBI) on HL-2A tokamak. A full solid-state RF generator with output power of 80 kW and frequency of 2 MHz was built by an RF combiner using 8 modules of solid-state RF generator with power of P RF = 10 kW. The line electric efficiency of whole RF generator reaches 92% and its voltage standing wave ratio (VSWR) is 1.01, thus no water-cooling system is supplied. A quartz vessel with the inner diameter of 250 mm is directly adopted for resisting atmospheric pressure, which can dramatically simplify source structure. Nowadays, the extracted beam parameters of RF hydrogen ion source are 32 kV/20 A/0.1 s on a test bed, while the design parameters are 50 kV/20 A/3 s. The beam density profile measured by the infrared imaging technique at 1.3 m downstream from the grounded grid obeys a Gaussian distribution, and the corresponding half width of 1/e power decay at the matched condition is about 80 mm. Plasma homogeneity is over 90% at low RF power. The beam divergence angle meets the requirement of NBI system on HL-2A tokamak. The extractable current density increases almost linearly with the RF power. It reaches 2400 A m−2 at P RF = 32 kW. The ion density in front of plasma grid is about 1 × 1018 m−3, corresponding to an ionized fraction of about 1% at the gas pressure of 0.5 Pa. Single hydrogen ion fraction reaches 79% at the beam current of 12.4 A. Some improvements have been considered for optimizing ion source performance on next experimental campaign. One smaller auxiliary RF discharge chamber equipped with a gas feed path, driven by 13.56 MHz/3.5 kW generator, is connected to main discharge chamber driven by 2 MHz/40 kW generator. By this dual-driven configuration, the innovative RF plasma source with high-pressure density gradient solves the initial ignition problem of powerful RF ion source even if the gas pressure below 0.1 Pa. In addition, the RF negative hydrogen ion source of 200 kV/20 A/3600 s is also developed at SWIP for the China fusion engineering test reactor.

Beaconless PAT and adaptive beam control using variable focus lens for free-space optical communication systems

Free-space optical communications (FSOCs) have recently emerged as a promising solution for various communication scenarios. However, the pointing, acquisition, and tracking (PAT) is a technically challenging issue, especially in airborne FSOC systems. In this paper, we present an adaptive beam control technique combined with beaconless PAT using a variable focus lens. By using the lens whose focal length can be tuned electrically, we facilitate the coarse PAT by enlarging the beam size and also mitigate the adverse effects of pointing errors by adjusting the beam divergence angle adaptively to the link conditions. The major benefit of the proposed scheme is that the beam control can be implemented in a simple and compact manner, without relying on mechanical movements. We carry out a proof-of-concept experimental demonstration of the proposed scheme for a 10-Gb/s free-space optical link over 104 m. The demonstration shows that the probability of PAT success can be improved considerably by using the proposed scheme. It also shows that the proposed scheme could result in a system loss reduction of 6.4 dB and improve the tolerance to pointing errors up to 500 μrad for a target bit-error ratio of 10−3. The response time of the lens is measured to be <211 ms. We confirm experimentally that the receiver size and the amount of pointing error determine the optimum beam size at the receiver.

Design and analysis of porous core photonic crystal fiber based ethylene glycol sensor operated at infrared wavelengths

A novel porous core photonic crystal fiber (PCF) sensor is reported for label-free detection of different concentrations of ethylene glycol present in aqueous solution, over a wavelength range from 1 to 2 μm. Both core and cladding are designed with elliptical air holes, which are arranged in a hexagonal structure with TOPAS as the background material. Various geometrical parameters are judiciously optimized to achieve an efficient sensor. Finite element analysis is employed for numerical simulation of the proposed structure, investigating various sensing parameters including effective refractive index, effective material loss, confinement loss, nonlinearity coefficient, shifts in peak reflected wavelengths, sensitivity, f-parameter, spot size and beam divergence angle. Simulation outcomes reveal a significant shift in the sensing parameters in response to changes in concentration of ethylene glycol, confirming the effectiveness of the sensor. Optimum wavelength sensitivity of 13,144.86 nm/RIU and resolution of $$7.46 \times 10^{ - 7}$$ RIU are attained, which provide a significant theoretical foundation for the design of novel photonic sensors. Benchmarking of the proposed PCF sensor is done against related research results to prove its superiority in terms of resolution and sensitivity.

16.9 MW, efficient 486.1 nm blue optical parametric oscillator using single BBO crystal

A single-resonant beta barium borate crystal optical parametric oscillator with high pulse energy output at the H-β Fraunhofer line of 486.1 nm was demonstrated. Pumped by a single-frequency 355 nm ultraviolet pulsed laser at 10 Hz repetition rate with maximum pulse energy of 411 mJ, maximum output energy of 162 mJ blue laser pulse at 486.1 nm was successfully obtained from a plano-concave cavity with a 40% output coupler, the corresponding optical-to-optical conversion efficiency was up to 39.4%, and the pulse width was around 9.6 ns. The blue laser beam size was 4.4 mm × 5.1 mm with the beam divergence angles of θx = 2.2 mrad and θy = 2.5 mrad. The peak power of output blue laser was 16.9 MW, and the signal linewidth was around 0.34 nm.