Maximum Signal Power Research Articles

Integrated erbium-doped waveguide amplifier on lithium niobate on insulator

The erbium-doped lithium niobate on insulator (Er:LNOI) has garnered significant attention as it combines outstanding gain property with integration capabilities, making it a promising solution for active devices on the versatile LNOI platform. This also paves a way for the development of appealing erbium-doped waveguide amplifiers. Here, we demonstrate an efficient integrated Er:LNOI micro-waveguide amplifier directly compatible with the lens fiber. In a 5.6-cm-long Er:LNOI micro-waveguide, we demonstrate a maximum internal net gain of 18.8 dB for 1531-nm signal light with 1460-nm pumping. Moreover, the maximum output signal power surpasses 20 mW, thereby confirming the practicality of the Er:LNOI micro-waveguide amplifier.

Broadband noise signal source positioning method using flat linear antenna in Fresnel zone near ‘water-air’ boundary

Ways of broadband noise signal reception using flat linear extended antenna in Fresnel zone near surface boundary enabling to determine direction, range to the source and depth of its immersion simultaneously with detection are considered. The effect emerging when signal source and receiver are located near «water-air» interface and two beams arrive from source to receiver (direct beam and beam reflected from the surface) is investigated. The supervisor of compensation of delays of signal arriving to M receivers of the antenna focuses receiving system in the point of the expected positioning of the source. In case of dual-beam signal it may result in emergence of two range focusing points in space. It is shown that focal spots may have high range spreading or practically merge depending on the relative positioning of the source and the receiver. Method of source submergence depth analysis at known ranges to two focal spots is offered for the first case. Method of consolidated signal processing which includes additional scanning of time delays in possible delays of signal between beams with uniform delay for all antenna elements is offered for the case when focal spots are not separated. It is demonstrated that when obtaining maximum signal power entered delay will be functionally connected with depth of immersion of the source that enables carrying out joint determining of direction, ranges and depths of submergence of the source in offered method. Moreover, it is demonstrated that method of consolidated processing enables to increase power of arriving signal up to 50 % in the point of maximum response as compared to conventional signal reception algorithm using flat linear antenna in Fresnel zone.

Optically biased and controlled signal processing in silicon photonics.

Optically biased and controlled signal processing is demonstrated in a commercial foundry silicon photonics integrated circuit process. Data and control signals are carried by different wavelengths in a WDM format. Optical signals on bias and control channels are converted to electrical voltages using series stacked photodiodes operating in photoconductive mode. Two examples of this scheme, namely, an amplitude modulator and a two-tap sequence detector capable of supporting different modulation formats, are experimentally demonstrated. The amplitude modulator requires 0.25 mW of optical control signal power to tune its optical output power by 15 dB. The two-tap sequence detector maps the consecutive symbols of a modulated signal such as OOK, PAM-3, and PAM-4, to distinct levels. A maximum control signal power of 5 mW is needed to calibrate and bias the sequence detector. This latter scheme may be extended to detect longer sequences and other modulation formats.

Brightness enhancement on random-distributed-feedback Raman fiber lasers pumped by multimode diodes

Abstract The power scaling on short wavelength (SW) fiber lasers operating around 1 μm are in significant demand for applications in energy, environment and industry. The challenge for performance scalability of high-power SW lasers based on rare-earth-doped fiber primarily lies in the physical limitations, including reabsorption, amplified spontaneous emission and parasitic laser oscillation. Here, we demonstrate an all-fiberized, purely passive SW (1018 nm) random-distributed-feedback Raman fiber laser (RRFL) to validate the capability of achieving high-power output at SWs based on multimode laser diodes (LDs) direct pumping. Directly pumped by multimode LDs, the high-brightness RRFL delivers over 656 W, with an electro-optical efficiency of 20% relative to the power. The slope efficiency is 94%. The beam quality M2 factor is 2.9 (which is ~20 times that of the pump) at the maximum output signal power, achieving the highest brightness enhancement of 14.9 in RRFLs. To the best of our knowledge, this achievement also represents the highest power record of RRFLs utilizing multimode diodes for direct pumping. This work may not only provide a new insight into the realization of high-power, high-brightness RRFLs but also is a promising contender in the power scaling of SWs below 1 μm.

Backward pumped distributed Raman amplifier: enhanced gain

The backward Raman amplifier (RA) can considered as one of the best solutions for optical communication, especially in Wavelength Division Multiplexing technology. They reduce the nonlinear effects, have low noise figure and a wide frequency range. The work in this paper aims to reduce the attenuation of optical signal due to its propagation optical fiber and increase both amplifier gain and output signal power. Two backward Raman models are proposed. Proposal one model consists of two cascaded RAs and the other (proposal two) consists of three cascaded RAs. Three backward pump power levels 200, 400, and 600 mW are used to simulate the models with the three types of fibers: single-mode fiber, Truewave, and Freelight, at an amplifier length of 100 km. Proposal two achieves a maximum gain of 31 dB at 600 mW pump power 600 mW using Truewave optical fiber, with 27.7 dBm maximum output signal power. This proposal is evaluated showing 11.15% gain enhancement and 200 mW saved power when compared to previously published work.

Development of a microwave resonant waveguide slot antenna with in-phase slot excitation

The object of research in the work is the process of radiation of electromagnetic waves of a resonant waveguide-slot antenna with in-phase excitation of slots. The subject of research is the wave parameters and directional properties of a resonant slotted waveguide antenna with in-phase slot excitation. The existing problem is that it is necessary to ensure highly directional properties of the antenna with electrical control of its wave parameters at high transmitter power. This problem is due to the fact that to solve the problem of developing equipment for radio control, and radar of aircraft, highly directional antennas of small sizes are required. To solve this problem, the paper proposes the design of a simple and cheap version of a microwave resonant waveguide-slot antenna with in-phase slot excitation.
 As a basis for developing a resonant slotted waveguide antenna, the authors chose a standard R48 rectangular waveguide, which is a classic in the theory of directional systems in the microwave range. This is due to the fact that in order to calculate and study a microwave resonant waveguide-slot antenna with in-phase excitation of slots, the authors used well-known elements of the theory of aperture antennas. The design of a resonant slotted waveguide antenna consists of a rectangular waveguide, an exciter, and a feeder. The radiation surface of the antenna is a wide wall of a standard R48 rectangular waveguide along the central axis, of which slots are symmetrically cut in a checkerboard pattern. The exciter is made in the form of a metal pin inside a rectangular waveguide near the short-circuited wall. This pin acts as an asymmetric vertical vibrator that excites electromagnetic waves in a rectangular waveguide. The antenna is tuned to the maximum radiation power mechanically by moving the short-circuited wall of the rectangular waveguide. The pin feeds a feeder based on a coaxial cable with a characteristic impedance of 75 ohms.
 The developed resonant waveguide-slot antenna with in-phase excitation of slots operates in the frequency range of 4.0–6.0 GHz. In the frequency range of 4.0–5.45 GHz, the value of Voltage Standing Wave Ratio (VSWR) varies from 1.08 to 2.1. In the frequency range of 5.45–6.0 GHz, the Voltage Standing Wave Ratio (VSWR) value varies from 2.1 to 6.55. The directivity of the antenna in the operating frequency range is not less than 90. The width of the main lobe of the antenna pattern in the horizontal plane is not more than 3.1°. The antenna gain in the operating frequency band is at least 100. The efficiency is at least 90 % with a maximum generator signal power of 10 kW.

Watt-level widely tunable narrow-linewidth pulsed mid-infrared MgO:PPLN optical parametric oscillator with a F-P etalon

A watt-level, widely tunable, narrow-linewidth pulsed MgO:PPLN optical parametric oscillator using a single etalon is demonstrated above 3 µm for the first time, to the best of our knowledge. The pump source is an acousto-optical Q-switched Nd:YAG laser at 1064 nm with a pulse duration of 220 ns and a repetition rate of 10 kHz. Employing a V-shaped cavity configuration, the emission wavelengths of the OPO can be tuned in the range of 3.64 µm − 3.8 µm and 1478 nm − 1503 nm by varying the temperatures of the MgO:PPLN crystal between 37℃ and 146℃. Under a pump power of 22.5 W, a maximum average output power of 2.12 W at 3.74 µm is achieved with a theoretical linewidth of 0.3 nm at the temperature of 79.6℃, corresponding to a pulse width of 145 ns and a peak power of 1.46 KW. At the same time, a maximum signal power of 2.86 W at 1486.66 nm is obtained with a linewidth of 0.03 nm, corresponding to a pulse width of 190 ns and a peak power of 1.51 KW.

Analysis of plantar impact characteristics of walking in patients with flatfoot according to basic mechanical features and continuous wavelet transform

Flatfoot is a common foot deformity, and the collapse of the arch structure affects the foot cushioning during walking. A growing number of scholars have found that the analysis of the impact force should be combined with both the magnitude and the frequency of the impact force. Therefore, the aim of this study is to investigate the plantar impact characteristics of flatfoot patients and normal foot people at different load-bearing buffer stage from the time and frequency domains. Sixteen males with flatfoot and sixteen males with normal foot were recruited to walk on the plantar pressure test system at the same step speed, and the vertical ground reaction force data were collected from the heel contact stage and the arch support stage. The differences in the frequency domain of the ground reaction force between the flatfoot and the normal foot in the two stages were analyzed according to the basic mechanical characteristics and the continuous wavelet transform. Independent sample t-test was used to compare the baseline data of subjects, and the differences in foot impact force characteristics at different stages of foot type and weight-bearing cushion phase were compared by two-factor repeated measures Analysis of Variance. 1) In terms of basic mechanical characteristics, In both groups for flatfoot patients and normal foot people, the peak ground reaction force was higher in the arch support stage compared to the heel contact stage (Pflatfoot<0.001, Pnormal foot<0.001), and the load rate of force change was smaller in this stage (Pflatfoot<0.001, Pnormal foot<0.001). However, no differences in peak ground reaction force and time of occurrence were found between flatfoot and normal foot in the two stages (p > 0.05), in the arch support stage, the force change load rate of patients with flatfoot was lower than that of normal foot people (p = 0.021). 2) The results of time and frequency domain characteristics showed that during the heel contact and the arch support stage, no significant differences in the maximum signal power as well as the corresponding time and the frequency of the main impact force between the normal foot and the flatfoot were found. In both flatfoot and normal foot types, compared with the foot heel contact stage, the maximum signal power in the arch support stage was higher (Pflatfoot < 0.001, Pnormal foot<0.001), and the corresponding impact frequency was smaller (Pflatfoot = 0.002, Pnormal foot = 0.004). Once the step speed was controlled, the flatfoot patients only showed a smaller impact force load rate in the arch support stage, which may be related to their lower arch rigidity. The characteristics of the impact force in different stages of walking support period were different in time and frequency domain, suggesting that there may be differences in the function of various parts of the foot.

Ideal single mode laser operation with single drive conventional/phase shift Mach–Zehnder modulators measured in optical access networks

Abstract The work outlined ideal single mode laser operation with single measured drive phase shift/conventional Mach–Zehnder modulators (MZM) in optical access networks is simulated and analyzed. Maximum signal power level versus spectral wavelength and time domain spectrum after fiber channel based 1.5 splitting ratio conventional/phase shift MZM and Idea single mode laser is measured accurately. Maximum Q coefficient of 35.87 and mini bit error rates of 2.3279 × 10−282 in the case of conventional MZM and idea single mode laser. Maximum Q coefficient of 17.86 and mini error rate of 1.0376 × 10−71 in the case of phase shift MZM and Idea single mode laser.

Spatial single mode laser source interaction with measured pulse based parabolic index multimode fiber

Abstract The study clarified spatial single mode laser interaction with measured pulse based parabolic index multimode fiber. Peak power level margin, maximum/minimum signal amplitude margin after parabolic index multimode fiber are measured with core radius of 25 µm, cladding thickness of 10 µm, refractive index peak of 1.4142, length of 300 m, and refractive index step of 1%. Maximum signal power margin against spectral frequency after PIN light detector based parabolic fiber properties is tested under the same operating parameters. The signal power amplitude/power within parabolic index multimode fiber is also measured based on variations of fiber lengths and relative refractive index step. The study implies the multimode graded index fibers with parabolic or near parabolic index profile cores have transmission bandwidths than other multimode fibers.

A 102 W High-Power Linearly-Polarized All-Fiber Single-Frequency Laser at 1560 nm

A 1560 nm high-power linearly-polarized all-fiber single-frequency narrow-linewidth laser with near diffraction-limited beam quality is demonstrated. The Yb–Er energy transfer efficiency and the ability of the signal laser to capture pump light have been improved by specifically choosing the pumping wavelength and the input signal power in the final power amplifier stage of this laser system. Under the off-peak absorption pumping wavelength of 940 nm, along with the maximum input signal power of 6 W, a maximum output power of 102 W with a slope efficiency of 40.5% is acquired. At the highest output power status, a polarization extinction ratio (PER) of 15.5 dB, a linewidth of 3.05 kHz, and a beam quality of Mx2 = 1.14, My2 = 1.06 are obtained, respectively. This advanced single-frequency fiber laser has great potential for the long-range coherent Doppler lidar and the next generation of gravitational wave detection.

Effects of Central and Peripheral Fatigue on Impact Characteristics during Running.

Fatigue and impact can represent an injury risk factor during running. The objective of this study was to compare the impact transmission along the locomotor system between the central and peripheral fatigued states during running. Tibial and head acceleration as well as shock attenuation in the time- and frequency-domain were analyzed during 2-min of treadmill running in the pre- and post-fatigue state in eighteen male popular runners (N = 18). The impact transmission was measured before and after a 30-min central fatigue protocol on the treadmill or a peripheral fatigue protocol in the quadricep and hamstring muscles using an isokinetic dynamometer. The time-domain acceleration variables were not modified either by peripheral or central fatigue (p > 0.05). Nevertheless, central fatigue increased the maximum (p = 0.006) and total (p = 0.007) signal power magnitude in the high-frequency range in the tibia, and the attenuation variable in the low- (p = 0.048) and high-frequency area (p = 0.000), while peripheral fatigue did not cause any modifications in the frequency-domain variables (p > 0.05). Furthermore, the attenuation in the low (p = 0.000)- and high-frequency area was higher with central fatigue than peripheral fatigue (p = 0.003). The results demonstrate that central fatigue increases the severity of impact during running as well as the attenuation of low and high components.

Phosphosilicate Fiber-Based Low Quantum Defect Raman Fiber Laser with Ultrahigh Spectral Purity.

The phosphosilicate fiber-based Raman fiber laser (RFL) has great potential in achieving low-quantum defect (QD) high-power laser output. However, the laser’s performance could be seriously degraded by the Raman-assisted four-wave mixing (FWM) effect and spontaneous Raman generation at 14.7 THz. To find possible ways to suppress the Raman-assisted FWM effect and spontaneous Raman generation, here, we propose a revised power-balanced model to simulate the nonlinear process in the low-QD RFL. The power evolution characteristics in this low-QD RFL with different pump directions are calculated. The simulation results show that, compared to the forward-pumped low-QD RFL, the threshold powers of spontaneous Raman generation in the backward-pumped RFL are increased by 40% and the Raman-assisted FWM effect is well suppressed. Based on the simulation work, we change the pump direction of a forward-pumped low-QD RFL into backward pumping. As a result, the maximum signal power is increased by 20% and the corresponding spectral purity is increased to 99.8%. This work offers a way for nonlinear effects controlling in low-QD RFL, which is essential in its further performance scaling.

High-efficiency 940- and 969-nm brightness-maintaining wavelength-multiplexed LD-pumped 240-W thin-rod Yb:YAG amplifier

A high-efficiency ultrafast laser amplifier based on thin-rod Yb:YAG was demonstrated, featuring a 940- and 969-nm brightness-maintaining wavelength-multiplexed laser diode (LD)-pumping method. Two high-brightness LDs (940 nm and 969 nm) were spectrally combined into one beam spatially with a dichroic mirror, thus enabling twice pump power while maintaining high brightness. A maximum signal power of 240 W was obtained at a repetition rate of 1 MHz, with a power extraction efficiency (PEE) of ∼51%. To the best of the authors' knowledge, this is the first report of >50% efficiency as well as the highest average power operating at the fundamental mode for thin-rod Yb:YAG amplifiers. The beam quality factors (M2) of the amplified signal were measured to be 1.72 and 1.12 for the horizontal and vertical directions, respectively. A preliminary pulse compression was conducted at a signal power of 80 W with a chirped volume Bragg grating (CVBG) compressor. The compressed pulse duration was 744 fs with an average power of 66.5 W, corresponding to a compression efficiency of 83.1%.

Tunable short-wave near-infrared continuous wave source based on a 532 nm pumped singly resonant optical parametric idler oscillator

We report a continuous wave (CW) singly resonant optical parametric idler oscillator (i-SRO) capable of providing high power, high power conversion efficiency, widely tunable radiation in the short-wave near-infrared (NIR) range. The i-SRO is pumped by a fiber-laser-based laser at 532 nm with a multi-grating, MgO doped periodically poled stoichiometric lithium tantalate (MgO:sPPLT) as quasi-phase matching (QPM) crystal. By utilizing eight grating periods, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, and 8.8 µm of the QPM crystal, with grating tuning and temperature tuning, the i-SRO can be continuously tuned across 951–793 nm and the corresponding idler tunable over 1212–1620 nm. A maximum signal power of 4.9 W for a pump power of 9.1 W and a relevant pump to signal conversion efficiency of ∼53.8% are achieved at the signal of 821 nm. At a pump power of 5.4 W, the output power stability of the signal at 837 nm is better than 2.1% rms, within one hour in Gaussian spatial beam profile. The SRO performance in tuning rate has also been investigated.

QAM receiver based on light amplifiers measured with effective role of optical coherent duobinary transmitter

Abstract Effective role of optical duobinary transmitter with optical coherent quadrature amplitude modulation (QAM) receiver based on light amplifiers measured is stimulated by using optisystem simulation software version 13. Signal, noise power levels are stimulated after long haul fiber optic range up to 350 km distance. Measured light amplifiers, optical duobinary transmitters and optical QAM receiver are employed to measure the peak signal amplitude power (SAP) and noise signal power for bit rate transmission with 100 Gb/s based 350 km length. Maximum signal power level margin is enhanced with high data rates transmission.

High efficiency holmium-doped triple-clad fiber laser at 2120 nm

We developed a new holmium-doped triple-clad fiber (Ho-3CF), reducing the clad diameter to improve the overlap between pump and doped-core, and the holmium concentration to reduce the influence of ion clustering on the laser efficiency. We illustrate here the performance of this fiber in a laser oscillator configuration. The laser emission is centered at 2.12&#x00A0;m by a fiber Bragg grating, and the active fiber is pumped in the clad by a 1.94&#x00A0;m thulium-doped fiber laser. The slope efficiency reaches 73&#x00A0;&#x0025; with respect to absorbed power (60&#x0025; considering coupled power), for a maximum signal power of 62&#x00A0;W delivered on a quasi single spatial mode (M<inline-formula><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula>=1.2). To the best of our knowledge, this slope efficiency is the highest reported for a high power clad-pumped fiber laser emitting at a wavelength higher than 2.1&#x00A0;m. We also analyze experimentally the impact of the pump Numerical Aperture (NA), at the input of the Ho-3CF, on the laser efficiency. Finally, we use our numerical simulation to comment on the best choice of pump wavelength.

Compact, 2.95-GHz repetition-rate femtosecond optical parametric oscillator with tunable pulse repetition frequency

We report a compact femtosecond optical parametric oscillator (OPO) with a tunable repetition rate that is harmonically pumped using a 52.5 MHz Yb-doped fiber laser system. By reducing the OPO cavity length, the repetition rate can be adjusted successively from 1.935 to 2.95 GHz at 52.5 MHz intervals. The multiplication of the repetition rate is achieved by placing a nonlinear crystal in a compact linear cavity, and the minimum cavity length is 47.8 mm. The maximum signal power (205.2 mW) at 2.04 GHz is obtained at an input pump power of 2.35 W and a central wavelength of 1472 nm. The central wavelength of the signal pulses can be tuned from 1383 to 1596 nm. To the best of our knowledge, 2.95 GHz is the highest repetition rate achieved using a femtosecond OPO based on an ultrashort cavity with a length that is N times (N is an integer) shorter than that of the pump cavity.

Improving the Efficiency of Information Flow Routing in Wireless Self-Organizing Networks Based on Natural Computing

With the constant growth of requirements to the quality of infocommunication services, special attention is paid to the management of information transfer in wireless self-organizing networks. The clustering algorithm based on the Motley signal propagation model has been improved, resulting in cluster formation based on the criterion of shortest distance and maximum signal power value. It is shown that the use of the improved clustering algorithm compared to its classical version is more efficient for the route search process. Ant and simulated annealing algorithms are presented to perform route search in a wireless sensor network based on the value of the quality of service parameter. A comprehensive routing method based on finding the global extremum of an ordered random search with node addition/removal is proposed by using the presented ant and simulated annealing algorithms. It is shown that the integration of the proposed clustering and routing solutions can reduce the route search duration up to two times.

Calculation of the formation of a network using antennas with a narrowly directed geometry of radio signal radiation

The field of wireless information transfer is relevant and important in the modern world. The ever-increasing amount of data that needs to be sent per unit of time is constantly growing, which inevitably increases the requirements for all components involved in the transportation of packages between subscribers. The text of the article provides a brief overview of the existing characteristics of receiving and transmitting devices, software for modeling and calculation of the signal pattern, for example, for ultra-shortwave transmission system. To perform such calculations, it is suggested to use common software, such as MATLAB and similar computer programs for mathematical calculations. This significantly speeds up the result and increases its accuracy. Carrying out such calculations at the stage of network design and construction with the use of remote signal propagation and reception allows to achieve the maximum signal quality and power, as well as to minimize the cost of time and money in the further implementation of the complex. To achieve the best result, the use of modeling the pattern of the signal propagated by an antenna with a narrow geometry of the radiation of radio waves is considered. The main and additional channels of such a means of transmission and their impact on the main characteristics of the system depend on the parameters of the antenna, its location and position. Therefore, by selecting these parameters, it is possible to change the influence of radiation from space and the Earth, which qualitatively affects the transmission of radio signals in such a system. In the future, rationally develop the proposed method in the design of radio transmission systems, which will further improve the results.