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This paper explores the propagation loss in waveguides on directly bonded InP/Si substrates, using numerical simulations to understand the effect of voids within the waveguide structure. Using COMSOL Multiphysics, we developed a model to simulate light propagation, focusing on how void characteristics such as diameter and angle influence the propagation loss. Our findings reveal a correlation between void dimensions and the increased threshold current density in separate confinement heterostructure multiple quantum well laser diodes, thereby providing insights into optimizing waveguide design for enhanced laser performance on InP/Si substrates. This research underscores the critical role of substrate bonding quality in minimizing internal losses and improving device efficiency. [ABSTRACT FROM AUTHOR]

This work reports on the possibility of sustaining a stable operation of polarization-doped InGaN light emitters over a particularly broad temperature range. We obtained efficient emission from InGaN light-emitting diodes between 20 K and 295 K and from laser diodes between 77 K and 295 K under continuous wave operation. The main part of the p-type layers was fabricated from composition-graded AlGaN. To optimize injection efficiency and improve contact resistance, we introduced thin Mg-doped layers of GaN (subcontact) and AlGaN (electron blocking layer in the case of laser diodes). In the case of LEDs, the optical emission efficiency at low temperatures seems to be limited by electron overshooting through the quantum wells. For laser diodes, a limiting factor is the freeze-out of the magnesium-doped electron blocking layer for temperatures below 160 K. The GaN:Mg subcontact layer works satisfyingly even at the lowest operating temperature (20 K). [ABSTRACT FROM AUTHOR]

The semiconductor laser (SCL) is a promising light source in photodynamic therapy (PDT). Overcoming the limitation of the low-penetration depth of PDT and enhancing its therapeutic effect on cancer treatment at a deep level requires enhancing the laser power beyond 100 mW in the CW and/or pulse mode. In this paper, we presented a theoretical guide for designing and optimizing SCL parameters to achieve high CW power and high-power short-time pulses to promote laser performance in PDT. High-power CW output was achieved by optimizing the parameters that control the light–current (L–I) characteristics. Picosecond high-power pulses were predicted based on the simulation of the laser signal under sinusoidal current modulation using the optimized CW parameters along with an appropriate selection of the modulation frequency and index signal class. The characteristics of the laser signal under intensive simulations over wide ranges of modulation frequency and index were used to classify the dynamic types of the laser signal. The operating domain of each of these types was mapped over a (modulation frequency versus index), and bifurcation diagrams were constructed to illustrate the flow among these domains. We spotted the variation of both peak power and pulse width of the periodic pulses with modulation parameters. CW output with power reaching ~ 360 mW was predicted using facet reflectivities of 0.01 and 0.99, cavity length as short as 120 µm, internal loss as small as 100 m−1, and confinement factor greater than 0.2. Periodic picosecond pulses with peak power reaching ~ 440 mW were predicted when the modulation index exceeds unity and the modulation frequency is higher than one-half of the relaxation oscillation. The pulse gets narrower with the increase in the modulation index and/or frequency. The obtained results would help design SCL with high power for efficient use in PDT. [ABSTRACT FROM AUTHOR]

Introduction: Laser treatment has been highly regarded for removing root canal microorganisms, which are the main causes of treatment failure. This study aimed to assess the effect of 810/980 nm diode laser irradiation on the reduction of Candida albicans (C. albicans) in the root canal. Material & Methods: In this experimental study, 25 healthy single-rooted human teeth were assigned to 20 test groups (two groups of 10), and 5 teeth were assigned to negative control groups. In the first group of the test, a rotary system and in the second group, a rotary laser diode were used to reduce the number of C. albicans. Two microliters of standard microbial suspension were added to each tooth and the samples were incubated (one week, 37°C, aerobic). Samples were taken from the teeth before and after instrumentation and cultured. The results were analyzed using Paired T-Test and T-Test. Results: The results pointed out that the number of yeasts showed a decrease of 92.2% (P

Blood vessel imaging provides crucial information for physiological monitoring and disease diagnosis. Optical‐resolution photoacoustic microscopy (PAM) is gaining intense attention in high‐resolution in vivo imaging of blood vessels. However, its applicability in clinical settings is hindered by the requirement of bulky and costly pulsed lasers as well as complex alignment procedures. Here, as a novel approach to high‐quality and cost‐effective microvasculature imaging, a dual‐wavelength fiber‐coupled laser diode‐based PAM (FC‐LD‐PAM) system is demonstrated on the mouse ear and brain in vivo. Furthermore, assisted with a deep learning method, the proposed technique effectively combines the advantages when using both small and large core‐size multimode fibers—successfully enhances the resolution of blurry mouse microvascular images obtained using a large core‐size fiber, revealing fine details that are comparable to those achieved using a small core‐size fiber; significantly reduces the overall time for data acquisition up to fourfold, improving the efficiency significantly in the imaging process. In addition, the proposed approach can achieve accurate and high‐resolution mapping of oxygen saturation in vivo, providing functional insight on living tissue. Therefore, the FC‐LD‐PAM can serve as a translational tool for high‐resolution imaging with enhanced accessibility and versatility in the biomedical field. [ABSTRACT FROM AUTHOR]

For realizing room‐temperature continuous‐wave operation in core–shell GaN nanowire‐based semiconductor lasers, certain device characteristics are required, namely, a low threshold current and low operating voltage. To reduce the operating voltage and inject current into the m‐plane multiquantum shell (MQS) active region, a new structure with a tunnel junction and embedded n‐GaN is proposed. One of the problems in this proposed device architecture is the high resistance at the tunnel junction layer due to hydrogen passivation in the insufficiently activated p‐GaN shell. In situ activation annealing and suppression of re‐passivation during subsequent growth are necessary to reduce the operating voltage. Herein, the time and temperature dependence of in situ activation annealing in a reactor to lower the resistance of tunnel junction layers grown on nanowires with nonpolar m‐planes is investigated. Subsequent n+‐GaN growth is implemented at 550 °C. As a result, the turn‐on voltage is observed to be dependent on the activation annealing time and temperature. The lowest turn‐on voltage is ≈5.4 V at an activation annealing time of 30 min and activation annealing temperature of 800 °C. [ABSTRACT FROM AUTHOR]

Optical fiber interconnects are playing a vital role in satisfying the demand for high-speed data transmission for long-range applications. The primary goal of the work presented here is to design an optical fiber communications system suitable for use at distances of up to 100 km. In this work, an intensity-modulated scheme at the transmitter and direct reception at the detector are employed to lower the overall system cost. Single-mode fiber (SMF) with nonlinearities is used as a transmission medium, connecting both transmitting and receiving sections. In order to get rid of the distortion brought on by the fiber, Bragg grating is used at the SMF's output. A Gaussian LPF is included in the receiver to eliminate the APD noise induced in the process of optical-to-electrical signal conversion. The performance of the system at 10 Gbps is assessed by examining the BER, Q-factor, and eye diagrams. The theoretical description of a Bragg grating is provided, and this work employs Optisystem softwarebased simulation. The results obtained reveal a BER value below 10-13 in the entire range of 100 km, in addition to the eye-opening factor of 0.85. [ABSTRACT FROM AUTHOR]

Introduction: Laser treatment has been highly regarded for removing root canal microorganisms, which are the main causes of treatment failure. This study aimed to assess the effect of 810/980 nm diode laser irradiation on the reduction of Candida albicans (C. albicans) in the root canal. Material & Methods: In this experimental study, 25 healthy single-rooted human teeth were assigned to 20 test groups (two groups of 10), and 5 teeth were assigned to negative control groups. In the first group of the test, a rotary system and in the second group, a rotary laser diode were used to reduce the number of C. albicans. Two microliters of standard microbial suspension were added to each tooth and the samples were incubated (one week, 37°C, aerobic). Samples were taken from the teeth before and after instrumentation and cultured. The results were analyzed using Paired T-Test and T-Test. Results: The results pointed out that the number of yeasts showed a decrease of 92.2% (P<0.001) and 94.5% (P<0.001), respectively, after instrumentation with the mentioned systems compared to before. On the other hand, there was a significant difference (P<0.01) between the rotary system and rotary laser after instrumentation. Discussion & Conclusion: Both methods effectively reduced the number of C. albicans from dental root canals, and the rotary laser system exhibited a significant (P<0.01) reduction in the number of yeasts compared to the rotary method. [ABSTRACT FROM AUTHOR]

Copyright of Micronanoelectronic Technology is the property of Micronanoelectronic Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Computer Measurement & Control is the property of Magazine Agency of Computer Measurement & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We are introducing an innovative organic semiconductor electroluminescent device capable of emitting light with unprecedented characteristics: high directionality (divergence angle of 1.1°) and high color purity (full width at half‐maximum of 2.5 nm). This achievement was realized through intricate design techniques aimed at enhancing gain via meticulous recombination zone control, complemented by the reduction of losses through minimizing the overlap of the optical mode with the electrodes. These groundbreaking results mark the world's first demonstration of simultaneously achieving a narrow spectrum and superior directionality in an organic electroluminescent device. [ABSTRACT FROM AUTHOR]

We are introducing an innovative organic semiconductor electroluminescent device capable of emitting light with unprecedented characteristics, that is, high directionality with divergence angle of 1.1° and high color purity with the full‐width at half‐maximum of 2.5 nm. This achievement was realized through design techniques aimed at enhancing gain via meticulous recombination zone control and complemented by the reduction of the optical losses. These results demonstrate the simultaneous achievement of a narrow spectrum and high directionality in an organic electroluminescent device. [ABSTRACT FROM AUTHOR]

Fiber pump lasers are widely used in a variety of fields, such as optical fiber communication, national defense, and medical beauty due to their high beam quality and intense laser energy. However, the alignment errors of optical parameters can influence the beam quality in the packaging of the fiber pump lasers. It is necessary to analyze the reflector, focusing lens, fiber, and the laser diode on the coupling influence between for guiding the fiber pump laser packaging. Firstly, we establish the optical path between the laser diode, focusing lens and reflector based on the physical ray-tracing method. On the other hand, the high coupling efficiency of whole system is achieved by optimize the parameters of each optical element. The simulation result shows that the highest coupling efficiency is 98.6% based on optimizing the parameters of the optical path while the experimental result of coupling efficiency is 90.36%. Also, the effects of refractive index, wavelength and fiber diameter on coupling efficiency are further investigated. The experimental results show that the radial displacement has the greatest influence on the coupling efficiency. The simulation results show that increasing the fiber core diameter can effectively improve the coupling efficiency. The results of rigorous analysis will provide an effective reference for manufacturing compact, high coupling efficiency fiber pumped laser. [ABSTRACT FROM AUTHOR]

Laser diodes (LDs) play an important role in our everyday lives. They are the smallest of all known lasers and have many common applications. It is important to recognize its characteristics and then improve them. One of the factors that greatly affects the laser intensity and its optical ability is the doping concentration (DC) of LD layers. Silvaco software was used to simulate ten layers of laser diode models based on (InP/InGaAsP) materials. The effect of doubling the DC of these models on the photon density (PD) and laser power (LP) was studied. Also, the shape of the spectrum generated as a result of changing the DC were investigated. The results showed that the (P-type) layers had a significant effect on the net doping (ND) as well as PD, which reached the highest value (17.2*107/cm3) at a photon energy (PE) of (1.02108 eV). The (N-type) layers have great affect to the emitted power of LD as reached to the value of (11.7 mW at anode current 1.4 mA/µm). The duplication process of the DC for all layers has a maximum range of ND (15.6-18.4)/cm3 and direct effect on PD of laser diode. Finally, this study explained briefly the powerful effects of increasing the doping process, especially the p-type, on the characteristics of LD devices, which were not addressed in previous studies. [ABSTRACT FROM AUTHOR]

Visible light communication is seen as a crucial technology within optical wireless communication systems. The technology of vehicular visible light communication holds significant importance in the context of connected vehicles. This technology can serve as a supplementary solution to vehicular systems that are based on radio frequency. In this paper, the authors conduct an analysis of the performance of both line-of-sight and non-line-ofsight vehicle-to-vehicle visible light communication systems under the effect of artificial light source and weather conditions, including clear, hazy, and foggy weather. A practical vehicular laser diode, a street lamp, and an avalanche photodiode are used to design the proposed system model. Performance enhancement for the proposed system is achieved using an optical amplifier at the receiving end. An artificial light source of light-emitting diode Corn-type is used to represent an ambient artificial light source. Different metrics such as quality factor and bit error rate are used to assess the system performance of the non-lineof-sight-vehicular communication system. The proposed line-of-sight model achieves a data rate of 25 Gbps, supporting a distance of 80 m under clear sky and hazy atmospheric conditions. For foggy weather, an attainable link distance of 70 m is achieved. The achieved results emphasize the suitability of the suggested models for vehicular applications in real world environment. [ABSTRACT FROM AUTHOR]

Visible light communication (VLC) is one of the fastest wireless communication systems compatible with 5G and beyond. Therefore, it was necessary to employ rapid modulation systems compatible with intensity modulation / direct detection (IM / DD), such as Flip-FBMC modulation technology. The distribution of illumination units across the entirety of the room poses the greatest difficulty for the VLC distribution system. Previous models suffered from dark spots or blind spots in the center of the room, which is the user's mobility area, as well as high power consumption, which is one of the most influential factors influencing the system. This is the first instance in which the illumination units are distributed in new locations by five lights installed in the ceiling in order to eradicate dark spots by using a laser diode (LD) instead of an LED due to its high-intensity illumination. The optimal semi-angle and field of view were calculated to be 43o and 45o, respectively, in order to obtain the best results in terms of the received optical power and the preferred performance of the SNR distribution in comparison to the previous models, as well as to improve the power consumption of the illumination units. using the optimal values of the semi-angle at 43° and FOV at 45°, the current findings indicate that Model 3 also attained the highest optical power received and the best SNR distribution performance compared to the previous models. In this way, a complete illuminate distribution is obtained for the room. [ABSTRACT FROM AUTHOR]

We present a high-efficiency continuous-wave Ho: LSO laser wing-pumped by a 1.91 μm laser diode. The impact of different output transmittances on the laser output power is compared and analyzed. The optimal result was achieved with a −500-mm radius curvature and a 6% transmission output coupler. The maximum output power of the Ho: LSO laser is 7.81 W, with a slope efficiency of 44.7%, a center wavelength of 2,106.6 nm, and beam quality factors of 1.4 in the x-direction and 1.3 in the y-direction.

In this publication a new approach to simulate the mode dynamics in broad-ridge laser diode is presented. These devices exhibit rich lateral mode dynamics in addition to longitudinal mode dynamics observed in narrow-ridge laser diodes. The mode dynamics are strongly influenced by higher order effects, which are described by effective interaction terms and can derived from the band structure and the carrier scattering in the quantum well. The spatial dependency of pump current densities plays a crucial role in lateral mode dynamics, and thus, a Drift-Diffusion model is employed to calculate the current densities with an additional capturing term.

High precision time-of-flight based light detection and ranging (LiDAR) system needs compact ultrafast pulsed lasers, such as gain-switched semiconductor laser diodes, which have the advantages of low cost, small size, and mass-producible, for short pulse generation, and are of great interest in many other fields, where low-cost high-voltage electrical pulse generators are in demand to directly modulate laser diodes for practical applications. Here, we presented a low-cost subnanosecond electrical pulse generator based on avalanche transistors, with output electrical pulses having a maximum peak voltage of approximately 25 V and a minimum pulse width of approximately 450 ps, depending on load impedance. We applied the electrical pulses on a gallium nitride (GaN)-based blue-violet laser diode, and demonstrated typical gain-switching characteristics of the laser diode. The minimum pulse width of the first spike of the gain-switched optical pulses was as short as 23 ps. In addition, we constructed a field-programmable gate array (FPGA)-triggered Marx generator with programmable frequency, and demonstrated its practicability in characterizing the transient gain-switching properties of laser diodes with a streak camera. These results should be of significant interest for both industrial applications and scientific research.

This work reports on the possibility of sustaining a stable operation of polarization-doped InGaN light emitters over a particularly broad temperature range. We obtained efficient emission from InGaN light-emitting diodes between 20 K and 295 K and from laser diodes between 77 K and 295 K under continuous wave operation. The main part of the p-type layers was fabricated from composition-graded AlGaN. To optimize injection efficiency and improve contact resistance, we introduced thin Mg-doped layers of GaN (subcontact) and AlGaN (electron blocking layer in the case of laser diodes). In the case of LEDs, the optical emission efficiency at low temperatures seems to be limited by electron overshooting through the quantum wells. For laser diodes, a limiting factor is the freeze-out of the magnesium-doped electron blocking layer for temperatures below 160 K. The GaN:Mg subcontact layer works satisfyingly even at the lowest operating temperature (20 K).

Possible conditions are considered for using the quantum formalism of PT symmetry when solving wave equations in systems with a pseudo-Hermitian Hamiltonian in order determine to the optical field structure and radiation spectra of modern high-power laser diodes. Physical mechanisms affecting the spatial and spectral separation of the radiation into separate channels of generation are discussed. [ABSTRACT FROM AUTHOR]

DFB diode laser at 1434 nm was used to detect the hydroxyl radical OH in the first overtone region. Experiments were made at the most intense line Q(3/2) of 2Π3/2 electronic term. Collisional broadening for He buffer gas was measured. Using reliably defined integrated intensity of this line and calculated line contour, the absorption cross section could be obtained for different pressures. This enables measurement of the absolute concentration of OH in time-resolved experiments without calibration. The minimum concentration of radicals detected by absorption is 2 × 1012 cm–3 with the resolving time approximately 10–6 s. [ABSTRACT FROM AUTHOR]

A theoretical investigation of coupling optics is presented in this paper based on ABCD matrix formulation in order to predict the coupling efficiency involving a laser diode (LD) and some identical single-mode circular core dispersion-shifted fiber (DSF) and dispersion-flattened fiber (DFF) with a cylindrical microlens (CML) in its tip. The authors derive analytical equations for the relevant coupling efficiency by assuming Gaussian distributions of the fields for both the source and the fiber under paraxial approximation. Further, in order to consider the non-Gaussian nature of the field of dispersion managed fibers, we employ spot size of Petermann II in our investigation. The investigations are made for two commonly used wavelengths, namely 1.3 and 1.5 μm. Our suggested technique demands extremely little computing for execution. For stimulation by a LD generating light of wavelength 1.3 μm, the maximum coupling efficiency (η) goes up to 94.41 percent. The proposed formulation also accounts for the limited aperture permitted by the CML. Thus, the analysis should find wide use in the design of CML on the single-mode circular core dispersion-controlled fibers tip to achieve large propagation distance. [ABSTRACT FROM AUTHOR]

A novel method for the generation of an optical frequency comb (OFC) is presented. The proposed approach uses a laser diode with optical feedback and operating at a specific nonlinear dynamic state named periodic window. In this case, the laser spectrum exhibits a feature with a series of discrete, equally spaced frequency components, and the repetition rate can be flexibly adjusted by varying the system parameters (e.g., external cavity length), which can provide many potential applications. As an application example, a dual-OFC system for distance measurement is presented. The results demonstrate the system's ability to achieve target distance detection, underscoring its potential for real-world applications in this field. [ABSTRACT FROM AUTHOR]

We performed measurements of laser beam power polarized in different angles as 0 ∘ , 45 ∘ and 90 ∘ passing close to a symmetric shielded capacitor with parallel plates and through a polaroid filter configured with angles as 0 ∘ , 45 ∘ and 90 ∘ . An unusual light power variation was detected during the charging and discharging of the high voltage capacitor even considering the suppression of known electromagnetic interaction between laser beam and capacitor. The light power variation curves also indicated a typical pattern of charge and discharge of capacitors. The combination of the angles of the laser beam polarization and polaroid filter surprisingly indicated the measurement of correlations between the polarizations of photons and electric dipoles of the capacitor dielectric. These novel results can only be explained supposing the preexisting condition of quantum entanglements between discrete observables of electric dipoles and photons. [ABSTRACT FROM AUTHOR]

Testing the effect of distance and laser beam heat on engraving results using two specimens as test materials, namely teak wood and durian wood. The testing process is to make circles and rectangles with a diameter of 20 mm which are inputted into the program followed by the engraving process. The results of the engraving are measured how many differences occur so that the results that are closest to the level of precision are obtained with variations in distance and heat in the laser beam. From the results of the distance test, it was found that durian wood has a more precise engraving accuracy with a size of 0.15-0.35mm, while for teak wood with a size of 0.2-0.4mm. With reference to the general tolerance of medium in sizes >6-30mm is 0.2mm, the best result for the use of spacing is 70mm. From the results of laser heat testing, it was found that durian wood has a more precise engraving accuracy with a size of 0.05 - 0.7mm, while for teak wood with a size of 0.1-0.8mm. With reference to the general tolerance of medium in size >6-30mm is 0.2mm and size >30-120mm is 0.3mm, the best temperature result for use is 400C with a tolerance size of 0.05mm.

The article considers a model of a free-space communication line between several closely located points on the terrain that are outside the line of sight. For the rapid deployment of communication lines with a range of up to hundreds of meters, any tall building visible to all callers can be a kind of optical signal repeater. Compared to radio communication channels, an optical communication line has a higher speed of information transmission, is insensitive to electromagnetic interference and is more protected from eavesdropping. To increase the range of the communication line and increase the signal to noise ratio, it is proposed to use a smart reflector based on the mirror of the two-axis scanner, the angular position of which is controlled by the microcontroller. The microcontroller receives information about the angle of incidence of the laser beam on the smart reflector in the form of photoelectric signals. These signals are formed by a position-sensitive photodetector and a lens in front of it. Depending on the angle of incidence of the laser beam, the position of the laser spot focused by the lens on the photodetector changes, and with it, both signals at its output. To facilitate the search of the smart reflector by transceivers, it is suggested to use an LED beacon in it.

Two complexes - derived from dithiocarbamate ligand (L) and their adduct with nitrogen base of the general formula [Cu(L)2], [Cu(L)2(A)] obtained by the condensation of CuCl2.2H2O with L= diisopropyl amine dithiocarbamate and A=1,10-phenanthroline weve directly been synthesized and characterized by infrared spectra, metal content and magnetic measurement. Some properties of these two complexes, including UV/VIS absorption, melting point, and molar conductivity measurement are characterized in both cases before and after applying laser diode radiation with an emission wavelength of 532 nm. It found that laser has potential effects on Cu complexes under investigation for specific conditions and doses where new complexes have been observed, and spectral data and magnetic measurement showed a tetrahedral and octahedral geometries for [Cu(L)2] and[Cu(L)2(A)], respectively [ABSTRACT FROM AUTHOR]

The results of a comparative study on how the design of multiple quantum structures containing a parabolic barrier profile affects optical properties are presented. All quantum well (QW) structures were grown by molecular beam epitaxy (MBE) on semi-insulating GaAs substrates. The investigated samples consisted of (i) double parabolic quantum wells (type A) or (ii) multiple (two or three) rectangular quantum wells surrounded by parabolic barriers (type B). The optical quality of samples was characterized performing room-temperature (RT-PL) and temperaturedependent photoluminescence (TD-PL) measurements. The investigation aimed at the optimization of a multiple quantum well (MQW) structure design for application in the gain region of near infrared (NIR) laser diodes (LDs) revealed benefits of both double parabolic quantum wells and a mixed design (rectangular MQW with parabolic barriers). The PL band position for all samples was registered in the vicinity around 1.19 eV, which corresponds to the Bi content in QW of ~4.4%. It was shown that all structures of type A exhibit an intense emission, while the intensity of photoluminescence measured for the samples of type B depends on the number of QWs. The weaker intensity of the PL signal from two QWs inserted between parabolic barriers was explained by a larger point defect density at low temperature grown inner GaAs barriers. The room-temperature PL intensity of the structure with three GaAsBi QWs embedded in one parabolic AlGaAs barrier was the highest one. The shift of PL peak position to lower energies (1.16 eV) was attributed to the slightly higher bismuth concentration, 4.9%. [ABSTRACT FROM AUTHOR]

Using the developed 2D numerical model of laser diodes, we study the effect of the cavity characteristics on the loss, and analyze the choice of the cavity parameters for efficient operation of the laser at ultrahigh pump currents. It is shown that at a fixed pump-current amplitude, a maximum output power is achieved for a combination of the optimal cavity parameters, namely, the cavity length Lopt and the output mirror reflectivity RARopt. It is found that the possibility of increasing the power by reducing the RAR coefficient is limited due to the formation of a local region of high optical loss and recombination loss currents near the cavity face with a high reflectivity. [ABSTRACT FROM AUTHOR]

This paper is dedicated to the modeling, design, and consequent construction of the practical setup of the small-size solid-state laser with Nd:YAG gain medium and the diode pumping. Solid-state lasers have been in existence for around 50 years and have experienced both positive and negative aspects during their evolution. Nevertheless, they have always held an essential position in numerous industries, scientific endeavors, and everyday activities. Nowadays, such devices are widely used and developed in location, manufacturing, medicine, and of course in military. Hence, the development and optimization of their structure remain a pertinent and important issue. The research reveals the basic component parameters for a compact Nd:YAG laser with diode pump, which can be implemented in the construction of range-finder. The main results of the work. Nd:YAG laser with overall dimensions of 350 x 25 x 25 mm was developed and modeled; the dimensions of the laser active head are 110 x25 x 25 mm. Diode pumping is a matrix of six diodes with a power of 90 W each, which operate in a pulse mode with a duration of 250 ns. The resonator consists of two mirrors, with an output reflectance from 0.66 to 0.74. The active element is 72 mm long. With these laser parameters, the first giant pulse after the start of pumping was achieved at 59 μs, an output energy of 25 mJ, and a laser system efficiency of 22 %. Additionally, the following radiation pulses were generated with a time interval of 4 μs. The results obtained in this work make it possible to create a diode-pumped solid-state laser with an output radiation energy of up to 25 mJ and have compact cavity dimensions of about 80 x 25 x 25 mm. [ABSTRACT FROM AUTHOR]

An improved technique for thermal resistance measurement of edge-emitting diode lasers using spontaneous emission spectra, collected through the opening in the n-contact within the range of operating currents, has been proposed. The advantage of the proposed technique is that systematic errors typical for measurements based on lasing spectra are excluded. The accuracy of the method was verified by measuring the dependence of the thermal resistance on the cavity length for diode lasers with 100 μm strip width. Obtained results are in good agreement with the model, and the minimum measurement error was ±0.1 K/W. The proposed technique can be used in metrological support of fabrication process of semiconductor lasers. [ABSTRACT FROM AUTHOR]

This paper proposes a self‐conducting current bypass circuit for series‐connected diodes in high power semiconductor light source. This circuit enables the main circuit current flow continuously, even if several of the diodes connected in series are open because of breakdowns. Herein, the composition, operation, and circuit design method of the proposed circuit are described. Moreover, the development of a simulation model of the fuse, which is an element of the circuit, is described. Furthermore, the simulation result of the proposed circuit using the fuse model is presented, and the method of determining the circuit constant based on the simulation result is demonstrated. Finally, by connecting a prototype circuit based on this study in parallel with series‐connected diodes, we show that the main circuit current of 60 A flow continuously even when one of the diodes is open. [ABSTRACT FROM AUTHOR]

Copyright of Orthodontie Française is the property of John Libbey Eurotext Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Frontiers of Information Technology & Electronic Engineering is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A robust and compact blue optical frequency reference within blue region was designed. A 40‐mW tellurium‐stabilized single‐frequency blue diode laser in external cavity was designed with an absorption spectroscopy method based on tellurium molecular transitions. Furthermore, the uncertainty of the frequency stabilization can be pushed to 2 × 10−9 at a 10‐s integration time. In addition, the correspondence frequency instability was 1.3 MHz when the laser wavelength was 445.75 nm. This study indicates that high‐stability frequency reference within the blue region can be achieved with an external cavity diode laser as opposed to the diode‐pumped frequency‐doubled solid‐state laser. [ABSTRACT FROM AUTHOR]

This article deals with frequency PWM (pulse-width modulation) control methodology and experiments related to a deep characterization of InGaN (Indium gallium nitride) EELs (Edge Emitting Lasers) and the influence of drive current shape on power and spectral characteristics. The aim is to study wavelength tuning possibility and near-threshold region behavior that is usually not described in device datasheets. The publication consists of three main parts where different possible methods of output control are discussed. The CW (continuous wave) characteristics are displayed in the first part which describes the behavior of the LDUT (laser diode under test) in more detailed manner than in the available datasheets. The following part shows PWM control with a delayed rising edge of the drive current which enables frequency control. The third part ultimately shows the behavior using PWM with a rectangular drive current shape.

Laser power transfer (LPT) is one of the leading technologies in long-distance power transmission with its advantages such as enabling high power transmission and suitability for mobile applications. The transmitter part, which includes the laser diode (LD) and the driving circuit, directly affects system efficiency. Continuous wave (CW) lasers are used in studies due to their high power and continuous radiation. However, one of the main disadvantage of the mentioned system is the high cost of LD. In this study, the use of pulsed LDs in LPT applications is proposed because of their small size and low cost. On the other hand, appropriate operating point of pulsed LD is missing information in the literature. In order to contribute literature with this information, pulsed LD is used for LPT, and the effects of driving voltage amplitudes, frequencies, and duty cycles are analyzed to demonstrate the importance of determining the appropriate operating point of the pulsed LD and the potential use of pulsed LDs in LPT.

Vehicular visible light communication is an emerging technology that allows wireless communication between vehicles or between vehicles and infrastructure. In this paper, a vehicular visible light communication system is designed using a non-return to zero on-off keying modulation scheme under the effect of different weather conditions such as clear, haze, and fog. The first model is a light emitting diode-based system and the second is a laser diode-based system. For both models, the influence of system parameters such as beam divergence, transceiver aperture diameters, and receiver responsivity is studied. The impact of the use of the trans-impedance amplifier is also investigated for both models. It was concluded that in the presence of the amplifier, output power of the light emitting diode and laser diode model are increased by 98.46 μW and 0.4719 W, respectively. The performance of the two proposed models is evaluated through bit error rate, quality factor, eye diagram, and output power to have some insightful results about the quality of service for the two proposed models. Under a specific weather condition, the performance of the system would be critical and other techniques should be applied. The maximum achievable link distance for the laser-based and light-emitting diode-based systems is 190 m at a data rate of 25 Gbps and 80 m at a data rate of 60 kbps, respectively, under the same system parameters and weather conditions. The obtained results provide a full idea about the availability of constructing our proposed model in a practical environment, showing a higher performance of the laser diode-based model than that of the light emitting diode-based model. [ABSTRACT FROM AUTHOR]

The introduction of visible light communication (VLC) technology could increase the capacity of existing wireless communication systems towards 6G networks. In practice, VLC can make good use of lighting system infrastructures to transmit data using light fidelity (Li-Fi). The use of semiconductor light sources, including light-emitting diodes (LEDs) and laser diodes (LDs) are essential to VLC technology because these devices are energy-efficient and have long lifespans. To achieve high-speed VLC links, various technologies have been utilized, including injection locking. Optical injection locking (OIL) is an optical frequency and phase synchronization technique that has been implemented in semiconductor laser systems for performance enhancement. High-performance optoelectronic devices with narrow linewidth, wide tunable emission, large modulation bandwidth and high data transmission rates are desired for advanced VLC. Thus, the features of OIL could be promising for building high-performance VLC systems. In this paper, we present a comprehensive review of the implementation of the injection-locking technique in optical communication systems. The enhancement of characteristics through OIL is elucidated. The applications of OIL in VLC systems are discussed. The prospects of OIL for future VLC systems are evaluated. [ABSTRACT FROM AUTHOR]

Fabry–Perot laser diodes based on (Al, Ga)As and Ga(As, Bi) with single or multiple parabolic or rectangular-shaped quantum wells (QWs) emitting at the 780–1100 nm spectral range were fabricated and investigated for optimization of the laser QW design and composition of QWs. The laser structures were grown using the molecular beam epitaxy (MBE) technique on the n-type GaAs(100) substrate. The photolithography process was performed to fabricate edge-emitting laser bars of 5 μm by 500 μm in size. The temperature-dependent power-current measurements showed that the characteristic threshold current of the fabricated LDs was in the 60–120 mA range. Light and current characteristics were almost linear up to (1.2–2.0) Ith. Low-frequency 10 Hz–20 kHz electrical and optical noise characteristics were measured in the temperature range from 70 K to 290 K and showed that the low-frequency optical and electrical noise spectra are comprised of 1/f and Lorentzian-type components. The positive cross-correlation between optical and electrical fluctuations was observed. [ABSTRACT FROM AUTHOR]

Periodontal disease is one of the most common chronic diseases in the oral cavity that causes tooth loss. Root scaling and leveling cannot eliminate all periodontal pathogens, and the use of antibacterial agents or lasers can increase the efficiency of mechanical methods. The aim of this study was to evaluate and compare the antibacterial activity of cadmium telluride nanocrystals in combination with 940-nm laser diode. Cadmium telluride nanocrystals were prepared by a green route of synthesis in aqueous medium. The results of this study showed that cadmium telluride nanocrystals significantly inhibit the growth of P. gingivalis. The antibacterial property of this nanocrystal increases with increasing its concentration, laser diode 940-nm irradiation and with increasing the time. It was shown that the antibacterial activity of combination of 940-nm laser diode and cadmium telluride nanocrystals is greater than the effect of either alone and can have a similar effect with its long-term presence of microorganisms. This is very important because it is not possible to use these nanocrystals in the mouth and in the periodontal bag for a long time. [ABSTRACT FROM AUTHOR]