Wavelength Of Laser Source Research Articles

Self-powered intelligent liquid crystal attenuator for metasurface real-time modulating

Triboelectric Nanogenerator (TENG) is capable of efficiently capturing mechanical energy and transforming it into electrical energy for self-powered systems, making it an ideal power source for Polymer Dispersed Liquid Crystal (PDLC). Herein, a Self-powered Intelligent Liquid Crystal Attenuator (SPILCA) is demonstrated for metasurface real-time modulating. The convergent beam-shaping metasurface consisting of holey meta-atoms with diameters ranging from 100 nm to 300 nm is fabricated by e-beam lithography (EBL). While the unique optical characteristics of the metasurface can be modulated within a certain frequency range, the E7 Liquid Crystal (E7-LC) has a large index of birefringence, and it can be powered by TENG to switch between two optical response states. Therefore, the combination of metasurface and SPILCA can achieve real-time control of metasurface by using the electricity regulatory of LC and the electromagnetic response of the metasurface. In order to build this SPILCA for metasurface modulating, a vertically contact-separated TENG based on Nylon electrospun film as triboelectric material is proposed. The maximum values of the open-circuit voltage, short-circuit current, transferred charge are 165 V, 25 µA, and 86 nC, respectively. By measuring the optical power and testing the modulation effect of SPILCA on the metasurface, it can be seen that the SPILCA has a good modulation effect on the optical signal, and even can reach 96 % intensity modulation when the laser source wavelength is 450 nm and the current is 0.09 A. This self-powered photoelectric response device does not require additional electrical power supply, and has great potential in future smart optical system design.

Performance optimization of PERC solar cells based on laser ablation forming local contact on the rear

Abstract To improve the photoelectric conversion efficiency (η) of the solar cell, a green wavelength (532 nm) laser source in a nanosecond range was used to ablate the passivated emitter and rear cell (PERC) to form the contact holes. If the laser ablation hole opening process was not set properly, the diameter or the external expansion of holes would be too large, causing the decline of the PERC performance. The Gaussian distribution of the laser is regulated by the output power (P o) and the repetition frequency (f rep) of the incident pulse laser, so that the optimized morphology of holes is obtained on the back of the PERC solar cells. After the contact holes are screen printed by the aluminum paste, the local back surface field is finally formed. The experimental results showed that the outward expansion decreases obviously with the increase of laser P o. Second, the spacing of the holes decreases with the increase of the laser f rep. It was found that under the laser P o of 33.0 W and f rep of 1,400 kHz, the η of the industrial PERC solar cells was the highest. The Quokka simulations indicated that small outward expansion, small diameter, and long spacing of holes would further decrease the recombination parameter in the rear surface. With the optimized morphology of contact holes and the low contact resistance, the PERC cell’s calculated V oc and η improvements were 6.5 mV and 0.48%, respectively, which was verified with experimental findings.

First results of CO2 dispersion interferometer on EAST tokamak

A dispersion interferometer (DI) has been installed and operates on the Experimental Advanced Superconducting Tokamak (EAST). This DI system utilizes a continuous-wave 9.3 μm CO2 laser source to measure line-averaged electron densities accurately. In contrast to conventional interferometers, the DI does not require substantial vibration isolations or compensating systems to reduce the impact of vibrations in the optical path. It also employs a ratio of modulation amplitudes, ensuring it remains immune to the variations in detected intensities. Without a variation compensation system, the DI system on EAST reaches a density resolution of less than 1.8 × 10−2π rad and a temporal resolution of 20 μs. The measurements made by the POlarimeter-INTerferometer (POINT) system and the far-infrared hydrogen cyanide (HCN) interferometer are remarkably consistent with the DI’s results. The possibility of fringe jumps and the impact of refraction in high-density discharge can be significantly decreased using a shorter wavelength laser source. A rapid density change of 3 × 1019 m−3 during 0.15 s has been measured accurately in shot No. 114755 of EAST. Additionally, the DI system demonstrates dependability and stability under 305 s long-pulse discharges in shot No. 122054.

Comparison of NLoS and LoS transmission techniques for UWOC using a 520 nm wavelength laser source

Comparison of NLoS and LoS transmission techniques for UWOC using a 520 nm wavelength laser source

Third-order nonlinear optical treatment of (Ni and Fe)-doped zeolitic imidazolate framework-67: Synthesize and characterization

A simple chemical reaction was applied for fast preparation of pure zeolitic imidazolate framework-67 (ZIF-67) and doped with Ni or Fe ions. The distinctive bands appeared in FT-IR spectrum of each samples confirmed the successful synthesis of ZIF-67 samples. The surface morphology and microstructure of prepared pure ZIF-67 were evaluated by TEM and SEM techniques. A rhombic dodecahedron skeleton with smooth surface was shown for the ZIF-67. The SEM images of ZIF-67 doped with Ni or Fe indicated a polyhedral shaped nanostructures smaller than 300 nm. Considering the XRD pattern, the crystallinity index of samples was calculated. The large optical nonlinearities of Ni, and Fe doping ZIF-67 were characterized using a 532 nm wavelength laser source. All synthesized samples showed the nonlinear refractive index and the nonlinear absorption coefficient in the order of 10−8 cm2/W and 10−5 cm/W, respectively. The crystallinity index and polarizability of (Ni, Fe)-ZIF-67 were increased in comparison with ZIF-67. The bigger ionic radius causes to have more electrons and raises polarization. The large two-photon absorption (TPA) and self-defocusing effect of Fe-ZIF-67 made it suitable for related applications in optical limiting devices.

Применение машинного обучения для детектирования фазы в когерентном оптическом рефлектометре

The work is aimed at solving the problem of phase detection in a phase-sensitive reflectometer when working with stochastic Rayleigh reflectors in the fiber. An improvement of measurement methods in coherent reflectometric systems, based on the use of machine learning algorithms, is proposed using a chirp reflectometer as an example. A chirp reflectometer with a tunable wavelength laser source was used to collect data necessary for training neural networks. The study shows that scanning by wavelength allows simulating various external effects, such as deformation or temperature changes over extended areas, thus ensuring efficient data collection for training. The use of even simple neural network algorithms leads to a significant increase in phase measurement accuracy by 43%, demonstrating the potential of this method for detecting phase of complex interferometric signals.

Silica micro-rod resonator-based Kerr frequency comb for high-speed short-reach optical interconnects.

Conventional data center interconnects rely on power-hungry arrays of discrete wavelength laser sources. However, growing bandwidth demand severely challenges ensuring the power and spectral efficiency toward which data center interconnects tend to strive. Kerr frequency combs based on silica microresonators can replace multiple laser arrays, easing the pressure on data center interconnect infrastructure. Therefore, we experimentally demonstrate a bit rate of up to 100 Gbps/λ employing 4-level pulse amplitude modulated signal transmission over a 2 km long short-reach optical interconnect that can be considered a record using any Kerr frequency comb light source, specifically based on a silica micro-rod. In addition, data transmission using the non-return to zero on-off keying modulation format is demonstrated to achieve 60 Gbps/λ. The silica micro-rod resonator-based Kerr frequency comb light source generates an optical frequency comb in the optical C-band with 90 GHz spacing between optical carriers. Data transmission is supported by frequency domain pre-equalization techniques to compensate amplitude-frequency distortions and limited bandwidths of electrical system components. Additionally, achievable results are enhanced with offline digital signal processing, implementing post-equalization using feed-forward and feedback taps.

Development of Luminescent Nd-Doped LaNbO Compound Thin Film Growth by Magnetron Sputtering for the Improvement of Solar Cells

Nd3+-doped LaNbO phosphor thin films were prepared by radio-frequency magnetron sputtering on Si substrates. The effects of a 1% Nd-doping concentration, after annealing at 1200 °C for 12 h, on the light-emitting properties of the sputtered thin films were characterized via several experimental techniques and deeply discussed. Photoluminescence characterization showed strong emission peaks typical of Nd3+ centers at 880 nm and 1060 nm when a 325 nm wavelength laser source was applied. Similar responses were detected in Nd3+-doped La3NbO7 powder samples fabricated by the solid-state reaction method. The coexistence of two phases (LaNbO4 and La3NbO7) in the thin films with higher nominal thickness was clearly identified based on different structural analyses. The promising results open the possibility for developing phosphor substrates as a preliminary step for the improvement of solar cells based on photon recycling mechanisms.

Terabit FSO communication based on a soliton microcomb

Free-space optical (FSO) communication technology is a promising approach to establish a secure wireless link, which has the advantages of excellent directionality, large bandwidth, multiple services, low mass and less power requirements, and easy and fast deployments. Increasing the communication capacity is the perennial goal in both scientific and engineer communities. In this paper, we experimentally demonstrate a Tbit/s parallel FSO communication system using a soliton microcomb as a multiple wavelength laser source. Two communication terminals are installed in two buildings with a straight-line distance of ∼ 1 km . 102 comb lines are modulated by 10 Gbit/s differential phase-shift keying signals and demodulated using a delay-line interferometer. When the transmitted optical power is amplified to 19.8 dBm, 42 optical channels have optical signal-to-noise ratios higher than 27 dB and bit error rates less than 1 × 10 − 9 . Our experiment shows the feasibility of a wavelength-division multiplexing FSO communication system which suits the ultra-high-speed wireless transmission application scenarios in future satellite-based communications, disaster recovery, defense, last mile problems in networks and remote sensing, and so on.

Improving image quality in diffuse optical tomography

Diffuse optical tomography (DOT) modality uses diffusion equation solution of low power laser distribution in the imaging tissue. DOT method has three main running mode and three geometric subbranches. Run modes are: Continuous Wave (CW), Time Resolved (TR) and Frequency Domain (FD) modes. These run modes might have transmission-through, back-reflected or ring geometry depend on the source and detector placements on tissue surface. In this work, we tested our novel imaging method on the frequency-domain back-reflected DOT simulation model. Our novelty is: selecting a great number of multi-frequency data in the wide frequency spectrum which was not tested before in the literature. Most of the literature works consist of narrow frequency band with the limited number of frequencies such as maximum 12 multi-frequency-data which cover from 100 up to 700 MHz. In our work, we tested and compared reconstructed inclusion images generated by our 500 wide spectrum multi-frequency data versus reconstructed inclusion images generated by 20 narrow band multi-frequency data which was generally used in FD DOT studies. We observed that our novel imaging method which used wide spectrum multi-frequency data is superior to the traditionally used narrow-band multi-frequency method based on the reconstructed inclusion image localization errors. Since most of the homogenous geometry consists of fat tissue, we selected background absorption coefficient µa = 0.2 cm−1 and tissue scattering coefficient $${\upmu }$$ s = 80 cm−1 for 800 nm laser source wavelength. Three-dimensional cubic imaging simulation media has 75-mm grid sizes in each direction. Two different imaging scenarios were tested. In the first scenario, one inclusion with absorption coefficient µa = 0.7 cm−1 was put inside the three-dimensional imaging geometry at 27 mm depth. In the second scenario one inclusion with absorption coefficient µa = 0.7 cm−1 was embedded in 48 mm depth location. Inclusions are cubic and they have 6 mm xyz length at each direction.

A Systematic Study of Laser‐Engineered Fluorescence in Carbon Black

The feasibility of laser-engineered fluorescence emission from carbon black (CB) with three laser sources of different wavelengths—660 nm (red), 532 nm (green), and 405 nm (blue) is demonstrated. From which the 660 nm focused laser beam produces the most intense fluorescence. Detailed systematic studies on how the laser-engineered fluorescence emission from CB depends on laser power, laser patterning speed, and environmental control during the laser modification process are carried out. From the systematic studies, the CB samples in ambience undergo most noticeable modifications with a laser power of ≈7 mW and patterning speed of ≈12 μms−1. The fluorescence emission is attributed to the creation of complex defects states into the oxidized form of the pristine system by the formation of 1) C60 fullerene and fullerites; 2) ZnO; 3) Zn2SiO4, and more complex hybrid such as 4) carbon-induced mid-gap states in Zn2SiO4, and 5) Ca-induced defects in ZnO. Such incorporations resulted in the formation of intermediate states in the large bandgap materials. As a result, distinct multicolored fluorescence is emitted by these laser-quenched material systems. Accordingly, multicolored fluorescence designs can be created with elaborative control of focused laser treatment in an ambient and helium environment.

Improved accuracy of eddy-current sensor based carrier lifetime measurement using laser excitation

In the manufacturing of modern solar cells, the early-phase quality inspection is crucial to detect harmful impurities and to reduce production waste. Thus, the charge-carrier lifetime measurement is beneficial before slicing the silicon ingot into wafers. Optimization of the widely used eddy-current detected photoconductance decay (e-PCD) technique for lifetime measurements is necessary to keep the pace with the new challenges appearing in photovoltaics. We investigated the dependence of the accuracy of the measurable carrier lifetime on the excitation laser parameters in the entire relevant carrier lifetime range. The complex behaviour of surface-recombination phenomena and its time evolution is studied by computer simulation. We optimized the components and parameters of the measurement setup and found that a 1064 nm laser is rather optimal compared to the 980 nm laser used previously. Using a longer wavelength laser source with elevated photon flux results in an improved accuracy of carrier lifetime recorded at Δn = 1015 cm−3 excess carrier concentration. A convincing similarity is found by comparing results from as-sliced and passivated surfaces. The optimized laser e-PCD method was compared to the flash-lamp based PCD method (known as QSSPC). Results agree very well for longer carrier lifetimes for which both systems evaluates the PCD curves in transient mode. However, for lower carrier lifetimes the universal transient mode operation of the e-PCD method is advantageous in terms of consistency.

High-performance self-powered photodetectors achieved through the pyro-phototronic effect in Si/SnOx/ZnO heterojunctions

Coupling together the pyroelectric effect and the photovoltaic effect is a novel method to significantly enhance the performance of photodetectors. In this work, we make use of this effect through a tri-layered heterojunction of n-Si/p-SnO x /n-ZnO, which takes advantage of the pyroelectric properties of the n-type ZnO film and the photovoltaic response of the n-type Si/p-type SnO x heterojunction. The photo-response of the device, with excitation from a 405 nm wavelength laser, is carefully investigated, and it is shown that the photodetector performance is improved with increased chopper frequency owing to the coupled photovoltaic-pyroelectric effect. The Al/Si/SnO x /ZnO/ITO device exhibits an optimum responsivity and detectivity of 36.7 mA/W and 1.5 × 10 11 Jones, respectively, with a laser power density of 36 mW/cm 2 and at a chopper frequency of 400 Hz. Ultrafast rise and fall times of 3 and 2 µs, respectively, were obtained. Moreover, by using a 650 nm wavelength laser source, the responsivity and detectivity were improved up to 64.1 mA/W and 2.4 × 10 11 Jones, respectively. The performance of these photodetectors is approximately twice as fast as other pyro-phototronic devices, and exhibits comparable photodetector characteristics when compared to perovskite/Si heterojunction and transition metal dichalcogenides lateral heterojunction devices. Therefore, by combining a pyroelectric ZnO film with a solar cell into one single structure, photodetectors based on the pyro-phototronic effect have been developed that demonstrate state-of-the-art performance. The devices show great promise for visible ultrafast photosensing. • Performance of the photodetectors are enhanced by coupling the photovoltaic and pyroelectric effects. • The pyro-phototronic effect is demonstrated for the first time in a n-p-n heterojunction. • An optimum responsivity and detectivity of 36.7 mA/W and 1.5 × 10 11 Jones were achieved at zero bias. • Ultrafast rise and fall times of 3 and 2 µs were achieved for Al/Si/SnO x /ZnO/ITO devices.

In Vivo Confirmation of Prostate Tumor Burden During HDR Brachytherapy With a Combined Raman Spectroscopy and MRI Radiomics Approach

<h3>Purpose/Objective(s)</h3> TRUS-guided biopsies still yield a notable rate of sampling error for prostate cancer (PCa) and do not allow <b>in situ</b> characterization. Raman spectroscopy (RS) is a minimally invasive optical imaging modality allowing to measure tissue properties within seconds. In this study, we present the first <b>in man r</b>esults from a navigated RS optical probe used to confirm sites of tumor burden during HDR brachytherapy. <h3>Materials/Methods</h3> The study included 8 prospectively recruited subjects with PCa prior to HDR brachytherapy. An electromagnetic (EM) guidance system was used to navigate <b>in vivo</b> RS acquisition using MRI-TRUS image fusion, and integrated within the HDR brachytherapy procedure workflow. The optical device includes a dual wavelength laser source (680 and 785 nm), a spectrometer, a custom design probe, and an acquisition/processing software. For each case, deformable registration of mpMRI (with prostate, urethra and GTV segmentations) to interventional 3D TRUS reconstructed images (with prostate and urethra segmentations), enabled visualization of GTV with the navigation system. The EM tracked RS probe was inserted through a co-axial needle. Once in place, high wavenumber (HW) and fingerprint (FP) spectra were measured, a biopsy was taken at the corresponding site, and the location was recorded; then, the HDR brachytherapy procedure resumed. Biopsy samples were evaluated histologically to confirm presence of cancer. For the radiomics analysis, 8 first order and 8 GLCM image features were calculated on the MRI (T2W and ADC), extracted from the corresponding optically scanned sites, using open-source software. <h3>Results</h3> In total, 26 sites were inspected with the RS probe and biopsied (range 2-5 per case). The pathology results identified 14 samples as cancer (Gleason score ≥ 7) and 12 samples as benign. On average the optical measurements took 45 seconds per site (range 23-90) and added 20 minutes (range 15-24) to the intervention. The spectra were pre-processed and labeled according to the pathology results. Neighborhood component analysis was applied to select the features that optimize the prediction performance, extracting 15 features from FP, 1 from HW and 11 from MRI radiomics. Classification models using a support vector machine were trained with a leave one out scheme for evaluation, using different feature combinations. Table 1 presents the average results over all folds. <h3>Conclusion</h3> We presented an image-guided system allowing the first <b>in situ</b> characterization of prostate lesions with RS during brachytherapy, in a manner integrated with the procedural workflow. The acquired spectra from benign and malignant regions show promising preliminary data, demonstrating the potential of the technique for real-time PCa confirmation. Finally, the combination of optical and MRI features yields an improvement in classification accuracy.

Computational Three-Dimensional Imaging System via Diffraction Grating Imaging with Multiple Wavelengths.

This paper describes a computational 3-D imaging system based on diffraction grating imaging with laser sources of multiple wavelengths. It was proven that a diffraction grating imaging system works well as a 3-D imaging system in our previous studies. The diffraction grating imaging system has advantages such as no spherical aberration and a low-cost system, compared with the well-known 3-D imaging systems based on a lens array or a camera array. However, a diffraction grating imaging system still suffers from noises, artifacts, and blurring due to the diffraction nature and illumination of single wavelength lasers. In this paper, we propose a diffraction grating imaging system with multiple wavelengths to overcome these problems. The proposed imaging system can produce multiple volumes through multiple laser illuminators with different wavelengths. Integration of these volumes can reduce noises, artifacts, and blurring in grating imaging since the original signals of 3-D objects inside these volumes are integrated by our computational reconstruction method. To apply the multiple wavelength system to a diffraction grating imaging system efficiently, we analyze the effects on the system parameters such as spatial periods and parallax angles for different wavelengths. A computational 3-D imaging system based on the analysis is proposed to enhance the image quality in diffraction grating imaging. Optical experiments with three-wavelength lasers are conducted to evaluate the proposed system. The results indicate that our diffraction grating imaging system is superior to the existing method.

Wavelength Dependent Odd Frequency Multiplication Based on a Superstructure FBG

In this letter, a photonic technique with wavelength tunable multiplication factor is proposed to generate odd multiple of modulating frequency. It is based on the cascading of two Mach-Zehnder modulators, super structured fiber Bragg grating, and a power combiner involving coherent heterodyne technique. Frequency tripling and quintupling of 10 GHz modulating signal have been demonstrated by tuning the wavelength of laser source and RF power control.The proposed scheme provides a simple method for photonic generation of widely tunable RF frequencies, and it has ability to change the multiplication factor by adjusting the wavelength of the laser source instead of tuning the passband frequency of the optical filter. The even multiplication capability of the proposed system can also be explored by changing the wavelength of the laser source.

Tunable multi-frequency optoelectronic oscillator based on a microwave photonic filter and an electrical filter

We propose and experimentally demonstrate a multi-frequency optoelectronic oscillator (OEO) based on the phase-modulation to intensity-modulation conversion. A microwave photonic filter incorporating an optical fiber Bragg grating Fabry–Perot filter and an electrical yttrium iron garnet (YIG) filter in two branches are used to select the oscillation modes of the OEO. By adjusting the wavelength of laser source or the central frequency of YIG filter, two frequencies can be tuned independently within a wide range. The single sideband phase noises of the generated frequencies are measured experimentally. Moreover, the OEO shows potential ability to achieve more frequencies oscillation by multiplexing more optical and electrical filters.

Heterodyne Standing-Wave Interferometer with Improved Phase Stability

This paper describes a standing-wave interferometer with two laser sources of different wavelengths, diametrically opposed and emitting towards each other. The resulting standing wave has an intensity profile which is moving with a constant velocity, and is directly detected inside the laser beam by two thin and transparent photo sensors. The first sensor is at a fixed position, serving as a phase reference for the second one which is moved along the optical axis, resulting in a frequency shift, proportional to the velocity. The phase difference between both sensors is evaluated for the purpose of interferometric length measurements.

Rainbow Archimedean spiral emission from optical fibres

We demonstrate a new practical approach for generating multicolour spiral-shaped beams. It makes use of a standard silica optical fibre, combined with a tilted input laser beam. The resulting breaking of the fibre axial symmetry leads to the propagation of a helical beam. The associated output far-field has a spiral shape, independently of the input laser power value. Whereas, with a high-power near-infrared femtosecond laser, a visible supercontinuum spiral emission is generated. With appropriate control of the input laser coupling conditions, the colours of the spiral spatially self-organize in a rainbow distribution. Our method is independent of the laser source wavelength and polarization. Therefore, standard optical fibres may be used for generating spiral beams in many applications, ranging from communications to optical tweezers and quantum optics.

Multi-user accessible indoor infrared optical wireless communication systems employing VIPA-based 2D optical beam-steering technique.

Infrared optical wireless communication system can achieve ultrahigh capacity and high privacy data transmission. However, for using narrow infrared laser beam as carrier to transmit signal, the high-speed data transmission can only be achieved by point-to-point connection. With the rapid number increasement of consumer electronic devices, such connection method puts a heavy burden on the number of transmitters. Thus, the transmitting end with the point-to-multipoint capability or multi-user accessibility is required. In this paper, we present a multi-user accessible indoor infrared optical wireless communication system employing passive diffractive optics based on a virtually imaged phased array (VIPA). Multiple beams can be generated in a point-to-multipoint scheme by using VIPA-based beam-steering antenna (BSA). On the other hand, by tuning wavelength of laser source, fast 2D steering of multiple beams with the same steering trajectory is supported, which can be used for user ends with changing locations. In the experiment, 5 beams are generated by utilizing only one transmitter. All five beams can realize 12.5 Gb/s on-off-keying (OOK) data rate transmission. Free-space optical wireless transmission at 3.6-m communication distance is demonstrated for system performance verification and evaluation. a total 3.44°×7.9° scanning field of view of five beams is achieved.