Laser Source Research Articles

A Long-Range Lidar Optical Collimation System Based on a Shaped Laser Source

Semiconductor near-infrared lasers have been widely used in lidar systems. However, various source types have different shapes and divergence angles, causing more difficulties for long-distance detection. In this paper, an optical collimation system is designed for a long-range lidar system with a shaped laser source (the wavelength is 905 nm, the emitted spot size is 50 µm long by 10 µm wide, and the divergence angles are 33°and 15°, respectively, which are unconventional). On the basis of the traditional method of aspheric lens setting, a pair of asymmetric aspherical lenses were designed using an extended polynomial. The simulation results show that the spot shapes are all close to circular from 100 mm to 30 m and the spot size always remains the same value. The corrected optical system is put into the designed lidar system for verification. It results show that the average divergence angles in the long and short axis directions are 0.06°and 0.07°, which satisfy the project requirements. This optical system designed provides a collimation scheme and expands the application of vehicle-mounted lidar in the field of long-range detection.

Facile nanofabrication and simultaneous color-and-Raman hybrid mechanism of economic SERS substrate with tunable structure color for high enhancement factor

The conventional SERS technique utilizing metal nanoparticles (MNPs) is a powerful optical sensing method, relying on the inelastic collision between incident light and the analyte. However, the development of traditional color-tunable MNP-SERS substrates remains limited to two separate components of the color supporter for generating structure color and followed by the MNPs coating to generate the localized surface plasmonic resonance for SERS sensing. Here, a novel color-tunable SERS substrate without MNPs based on the economic one-step anodic aluminum oxide (AAO) coated with nanoporous Pt films was proposed to generate the color-and-Raman hybrid effect for high enhancement factor. This novel SERS substrate employs an economic method, that is a facile and low-cost one-step anodization process to fabricate the AAO with tunable structure color, enabling adaptation to excitation of laser sources. The substrate with the lowest reflectance to laser light exhibits the highest enhancement factor due to the coupling between the laser and the substrate. The resultant SERS substrate demonstrates a high enhancement factor (EF) of 5.27x105 to methylene blue with a good uniformity of the relative standard deviation (RSD) of 6.35 %. In a practical application, one of preservative, benzoic acid, was detected with a low concentration of 1 ppm in the extraction solution of tapioca balls. This innovative approach promotes limitations associated with traditional color-tunable SERS substrates and offers a promising path for sensitive and versatile trace substance detection.

1.645 µm Er:YAG single-mode dual-wavelength emitter for CH4 differential absorption lidar.

We present a hybrid fiber/bulk laser source at 1.645 µm designed for methane (CH4) monitoring using differential absorption lidar (DIAL) measurements in the atmosphere. The emitter is also suited for coherent wind Doppler lidar. It relies on a Q-switched Er:YAG ring cavity pumped by erbium fiber lasers at 1532 nm. The pulsed laser is sequentially seeded by two fiber-coupled CW distributed feedback (DFB) laser diodes in the center of the CH4 line multiplet at 1645.55 nm (ON wavelength) and out of at 1645.30 nm (OFF wavelength). Despite a gain difference in the crystal between the ON and OFF wavelengths, pulses with equal energies and durations (9 mJ/300 ns) are obtained at a rate of 1 kHz. The spectral stability and purity properties in the dual-wavelength operating regime are presented.

Real-time acousto-optic imaging using high-peak-power long-pulsed illumination.

Acousto-optic imaging (AOI) of absorbing objects embedded in highly scattering media remains challenging, since the detectable signal suitable for image reconstruction is weak. To increase the detected signals to a level required by live biological applications, we designed a high-peak-power quasi-continuous laser source based on the coherent combination of two pulsed amplifiers, delivering 100-µs-long pulses with a 9 W peak power at a 100 Hz repetition rate while maintaining an average power below 100 mW; jointly used with a digital holographic detection that maximizes the amount of collected signal, we demonstrate for the first time to our knowledge the optical imaging of 2-cm-thick highly scattering media (µs' ∼ 10 cm-1) at near-video frame rate (0.2 Hz) using the Fourier transform-AOI.

Compact multi-port multi-wavelength laser source with Tbps transmission for optical I/O technology

In this paper, we propose and experimentally demonstrate a novel compact multi-port multi-wavelength laser source (MP-MWL) for the optical I/O technology. The multi-wavelength DFB laser array is used for realizing the simultaneous emission of multiple wavelengths. The reconstruction equivalent chirp technique is used to design and fabricate the π-phase shifted DFB laser array to achieve precise wavelength spacing. The number of wavelengths is enlarged through the monolithically integrated wavelength routing architecture (WRA), and 64 optical carriers are obtained with 8 wavelengths in 8 output ports. The proposed MP-MWL has high mode stability and high uniform wavelength spacing. The side mode suppression ratio (SMSR) of each wavelength is more than 40 dB and the wavelength spacing is 100 GHz under 25 °C working environment. A semiconductor optical amplifier (SOA) is monolithically integrated into each output port to amplify the output power. The output power of each port exceeds 15 mW when the current injected into the SOA is 150 mA. Besides, the relative intensity noise (RIN) of all wavelengths is below −130 dB/Hz, and clear 25 Gb/s NRZ eye grams are obtained for the 64 optical carriers with the external lithium-niobate Mach-Zehnder modulator, with a total transmission rate of 1.6 Tbps. The superior performance of the proposed MP-MWL enables it to be a promising approach for the Tbps optical I/O links and high-density chip interconnection system.

Sub-20 kHz low-frequency noise near ultraviolet butt-coupled fiber Bragg grating external cavity laser diode

We present a butt-coupled InGaN fiber Bragg grating (FBG) semiconductor laser diode operating below 400 nm in the single-mode emission regime. This compact coherent laser source exhibits an intrinsic linewidth of 14 kHz in the near-UV range and a side-mode suppression ratio reaching up to 40 dB accompanied by almost 2 mW output power. Furthermore, the properties of the FBG, including its central wavelength, bandwidth, and reflectivity, can be readily customized to fulfill specific requirements. As a result, the small footprint design of this laser is compatible with integration into a standard butterfly package to ease the lab-to-market technology transfer. The combination of low-frequency noise and fibered output signal positions these FBG laser systems as strong candidates for hybridization with integrated photonic platforms tailored for quantum information processing and metrology.

Figure-8 mode-locked Yb-doped fibre oscillator with a nonlinear amplifying loop mirror and power amplification

Abstract We report an all-polarization-maintaining Yb-doped fibre (YDF) femtosecond (fs) laser source at ∼1 µm comprising a figure-8 mode-locked oscillator and two YDF amplifier stages. By employing a nonlinear amplifying loop mirror, we could achieve dissipative soliton mode-locking with an output of 24.6 mW at a repetition rate of 6.2 MHz. In our experiments, a Raman signal of 16% in the pulse energy helps to obtain stable mode-locked operation in the figure-8 oscillator. The dissipative soliton pulse from the oscillator is stretched by a chirped fibre Bragg grating and is amplified by a two-stage YDF amplifier. After compression, the YDF master-oscillator power-amplifier system yields fs pulses with a pulse energy of 2.3 µJ and a pulse duration of 274.6 fs at a repetition rate of 0.52 MHz. The output pulse energy is limited by the third-order nonlinearity of the fibre amplifier chain. Prospects for further pulse energy scaling are discussed.

A review of label-free photonics-based techniques for cancer detection in the digestive and urinary systems

Abstract For a long time, it has been known that optics can provide a broad range of tools for addressing clinical needs, particularly diagnostics. Optical techniques can help in identifying diseases and detecting pathological tissues with non/minimally invasive and label-free methods. Given the current limitations of standard clinical procedures, such an approach could provide a powerful tool in detecting gastrointestinal and bladder cancers. However, each technique has serious limitations regarding one or more of the following features: biomarker sensitivity, penetration depth, acquisition times, or adaptation to the clinical environment. Hence there is an increasing need for approaches and instruments based on the concept of multimodality; in this regard, we review the application of different imaging/spectroscopy tools and methods operating in the first two optical windows (SHG, SPEF, TPEF, THG, 3PEF, CARS, Raman and reflectance) for tumour detection in the digestive and urinary systems. This article also explores the possibility of exploiting the third bio-tissue transmission window (1600-1900 nm) by reviewing state of the art in ultrafast laser sources development. Finally, we summarise the most recent results in developing multiphoton endoscopes – a key element for clinical in vivo translation of photonics-based diagnostics.

Simple theranostics nanoagent for precision suppression of tumor growth and metastasis: A traditional fermented product having a novel functional breakthrough

Biomass-based nanoagents constitute a focal point in the clinical development of tumor nanotheranostics, characterized by their high biocompatibility, biodegradability, controllability, and sustainability. However, achieving satisfactory nanoagents with biological safety and high theranostic efficacy for clinical translation remains a significant challenge. Herein, based on the design concept of medicine food homology, we developed a simple, mass-produced theranostics nanoagent (HSAVMn@CM NA) using Shanxi aged vinegar (SAV) as the raw material, enabling second near-infrared fluorescence/photoacoustic (NIR-II FL/PA) imaging-guided photo/catalytic/chemodynamic synergistic tumor therapy. A novel strategy involving the hydrolysis of SAV (HSAV) via the hydrolysis-acidification method has been developed to enhance NIR-II FL imaging performance. The HSAVMn@CM NAs have improved tumor-targeted efficiency through biomimetic modification of tumor membranes. Guided by NIR-II FL/PA dual-modal imaging, the HSAVMn@CM NAs achieve targeted photothermal/photodynamic synergistic phototherapy. Notably, the employment of a single laser source for simultaneous photothermal/photodynamic therapy has led to an enhancement in the efficacy of phototherapy. Moreover, the HSAVMn@CM NAs effectively chelated Zn2+ ions within the tumor microenvironment, to inhibit matrix metalloproteinase 2/9 (MMP 2/9) activity, thereby synergistically suppressing primary tumor growth and metastasis. Taken together, this research provides a novel design strategy for biomass-based nanoagents with potential clinical translation in precise tumor theranostics.

Switchable Dual-Wavelength Fiber Laser with Narrow-Linewidth Output Based on Parity-Time Symmetry System and the Cascaded FBG

In this paper, a dual-wavelength narrow-linewidth fiber laser based on parity-time (PT) symmetry theory is proposed and experimentally demonstrated. The PT-symmetric filter system consists of two optical couplers (OCs), four polarization controllers (PCs), a polarization beam splitter (PBS), and cascaded fiber Bragg gratings (FBGs), enabling stable switchable dual-wavelength output and single longitudinal-mode (SLM) operation. The realization of single-frequency oscillation requires precise tuning of the PCs to match gain, loss, and coupling coefficients to ensure that the PT-broken phase occurs. During single-wavelength operation at 1548.71 nm (λ1) over a 60-min period, power and wavelength fluctuations were observed to be 0.94 dB and 0.01 nm, respectively, while for the other wavelength at 1550.91 nm (λ2), fluctuations were measured at 0.76 dB and 0.01 nm. The linewidths of each wavelength were 1.01 kHz and 0.89 kHz, with a relative intensity noise (RIN) lower than −117 dB/Hz. Under dual-wavelength operation, the maximum wavelength fluctuations for λ1 and λ2 were 0.03 nm and 0.01 nm, respectively, with maximum power fluctuations of 3.23 dB and 2.38 dB. The SLM laser source is suitable for applications in long-distance fiber-optic sensing and coherent LiDAR detection.

Implementation of Optical Coherent Communication System between Two Computers

This work represents implementation and investigation of optical coherent communication system between two computers. A single mode optical fiber is selected as transmission medium. The data are sent via the RS-232 standard interface with a bit rate of 9.6 kbps from personal computer (PC1) by line receive to convert the data from electrical levels (-12/+12 V) into TTL level (0/5 V). The modulation of this data was accomplished by internal modulation using laser diode type (HFCT-5208M) 1310 nm wavelength. The optical D-coupler was used to combine the optical signal that come from laser source with optical signal of laser local oscillator (OTS-304XI) at 1310/1550 nm wavelength to obtain coherent (homodyne and heterodyne) detection respectively. A PIN photodetector (HFCT-5208M) is used. Calculations of Signal to Noise Ratio (SNR) and Bit Error Rate (BER) for coherent detection were measured at different length of the optical fiber. Result show that high SNR and low BER for heterodyne detection than for homodyne detection.

Topological-charge-tunable and wavelength- switchable vortex laser enabled by a helically twisted high-absorption few-mode erbium-doped fiber.

Vortex beams carrying orbital angular momentum (OAM) offer a solution for enhancing spatial degrees of freedom, particularly in conjunction with wavelength division multiplexing, which can significantly boost data capacity for optical communication. Addressing the increasing demand for high information-carrying capacity, we present a dynamically tunable OAM laser source in this study. We demonstrate a ring-cavity vortex fiber laser employing intra-cavity mode conversion through a helically twisted high-absorption few-mode erbium-doped fiber (HA-FM-EDF). The constructed vortex fiber laser exhibits wavelength switchability via an integrated Sagnac loop, facilitated by a homemade ring-core fiber. Furthermore, topological-charge tunability is achieved through the utilization of twisted HA-FM-EDF with varying helical pitches. To our knowledge, this marks the first successful implementation of two-dimensional multiplexing of wavelength and OAM in a vortex fiber laser. The OAM laser serves as a versatile vortex source with high tunability and flexibility, holding significant potential for deployment in ultrahigh-speed/ultrahigh-capacity communications, ultrahigh-resolution imaging, and ultrahigh-sensitivity sensing applications.

Fabrication of SnSe nanostructures visible light photodetectors

Tin selenide (SnSe), a potential low-cost material for technological use, possesses good optical, electrical, and optoelectronic properties. In the present study, thermally evaporated SnSe thin films with vertically grown nanosheet morphology are used to fabricate photoconductor-type photodetectors for visible light detection. The as-deposited films at room temperature (RT) are annealed in a vacuum from 100 to 250 °C and are investigated by EDX, XRD, Raman, FE-SEM, and UV–visible spectroscopy. The morphology and crystallinity of films that had been annealed at 200 °C were better, with (111) plane being the preferred orientation. From the optical transmittance measurements, the absorption coefficient and optical bandgap (Eg) of the deposited films were determined. Here, photo-sensing parameters of the detectors fabricated by depositing Ag contact and tested systematically using a 532 nm laser source of varied power intensities (1–5 mW/cm2) are reported. The photodetector’s performances were evaluated, and the fabricated film annealed at 200 °C had a responsivity of 25 × 10−2 AW−1, a peak EQE of 83 %, and an elevated detectivity of 30 × 108 Jones. The response speed of the fabricated photodetector was reasonably good with τr = 3.8 s and τf = 4.4 s under 5 V bias. The research showed the potential SnSe thin films might be used in the field of detecting visible light.

Directly modulated FMCW tunable laser with highly linear frequency chirp and narrow linewidth

Frequency-modulated continuous-wave light detection and ranging (FMCW LiDAR) is a promising technology for long-range, high-accuracy, stray-light-immune distance and velocimetry sensing. To achieve this, a precisely chirped and highly coherent laser source is required. In this work, we propose to generate a highly linear frequency chirp by utilizing an intracavity phase modulator with high linearity and demonstrate a proof-of-concept fully integrated monolithic FMCW laser source based on an InP generic platform. By electrically modulating the intracavity phase modulator at a repetition rate of 100 kHz, a 1.85 GHz chirp range with root mean square (RMS) frequency nonlinearity down to 1.8 MHz is achieved without the need of external feedback loop or predistortion. Meanwhile, the laser shows a 51 nm tuning range with a linewidth down to 16 kHz. By taking advantage of the high-speed electro-optical effects, fast frequency modulation with repetition rate of up to 1 MHz is realized with a frequency chirp range of ∼1.65 GHz and RMS frequency nonlinearity of ∼12 MHz. We demonstrate its feasibility for LiDAR through in-fiber ranging at a distance of 50 m, where a 51 cm resolution is directly achieved.

Compound parabolic concentrator for LED-based underwater optical communication transmitter

Laser sources have been used at the transmitter unit of underwater wireless optical communication (UWOC) systems since their invention. In recent years, light-emitting diodes (LEDs) have begun to be used as UWOC transmitters due to their low cost, long lifespan, and high energy efficiency. However, data transmission distances in UWOC systems using bare LEDs and LED arrays with collimating lens are limited due to LED’s large divergence angles and insufficient gains provided by the low cost lens designs. In this paper, we propose to use a compound parabolic concentrator (CPC), whose transmission efficiency curve is very close to the ideal concentrator, as a collimator that narrows the divergence angle of LEDs to design low-cost UWOC transmitter with long communication distance. Using the Bouguer–Beer–Lambert channel model, we derived the received optical power expression at the receiver side for the LED-based UWOC system with CPC at the transmitter. Furthermore, unlike existing studies in the literature, the full spectrum of the LED has been taken into account when deriving the power expression. The results show that using the CPC collimator instead of a typical collimation lens in an LED-based UWOC system can narrow the divergence angle by approximately 10 times, resulting in a 70 dB increase in signal-to-noise ratio (SNR) at the receiver and up to a 20 times increase in the communication distance.

In Vitro Comparison of Pulsed-Thulium:YAG, Holmium:YAG, and Thulium Fiber Laser.

Objective: To characterize the pulse characteristics and risk of fiber fracture (ROF) of the pulsed-Thulium:YAG (p-Tm:YAG) laser and to compare its ablation volumes (AVs) against Holmium:Yttrium-Aluminium-Garnet (Ho:YAG) laser and Thulium fiber laser (TFL). Materials and Methods: p-Tm:YAG (100 W-Thulio, Dornier-Medtech©, Germany) was characterized using single-use 272 μm core-diameter-fibers. p-Tm:YAG characterization included pulse shape, duration, and peak power (PP) studies. ROF was assessed after 5 minutes of continuous laser activation (CLA) at five decreasing fiber bend radii (1, 0.9, 0.75, 0.6, and 0.45 cm). p-Tm:YAG, Ho:YAG (120 W-Cyber-Ho, Quanta®, USA), and TFL (60 W-TFLDrive, Coloplast®, Denmark) AVs were compared using a 20-mm linear CLA at 2 mm/second velocity in contact with 20 mm3 hard stone phantoms (HSP) and soft stone phantoms (SSP) (15:3 and 15:5 water to powder ratio, respectively) fully submerged in saline at 0.5 J-20 Hz or 1 J-10 Hz. After CLA, phantoms underwent three-dimensional (3D) micro-scanning (CT) and subsequent 3D segmentation to estimate the AVs, using 3DSlicer©. Each experiment was performed in triplicate. Results: p-Tm:YAG presents a uniform pulse profile in all of the available preset modes. PP ranged from 564 to 2199 W depending on pulse mode. No laser fiber fracture occurred at any bend radius. p-Tm:YAG achieved similar mean AVs to TFL and Ho:YAG for HSP (8.96 ± 3.1 vs 9.78 ± 1.1 vs 8.8 ± 2.8 mm3, p = 0.67) but TFL was associated with higher AVs compared with p-Tm:YAG and Ho:YAG (12.86 ± 1.85 vs 10.12 ± 1.89 vs 7.56 ± 2.21 mm3, p = 0.002) against SSP. AVs for HSP increased with pulse energy for p-Tm:YAG and Ho:YAG and (11.56 ± 1.8 vs 6.36 ± 0.84 mm3 and 11.27 ± 1.98 vs 6.34 ± 0.55 mm3, p = 0.03 and p = 0.02), whereas AVs for SSP were similar across laser settings for all laser sources. AVs with TFL were similar across laser settings for both phantom types. Conclusion: p-Tm:YAG combines intermediate PP between Ho:YAG and TFL, a uniform pulse profile, no ROF with increasing deflection and effective ablation rates. Further clinical studies are needed to confirm these in vitro results.

Effect of laser beam incident angle on welding of Ti6Al4V with fiber lasers

Laser beam welding (LBW) is widely used for welding Ti6Al4V alloys in aerospace applications. LBW has localized high-energy fluence with low-energy input compared to other fusion welding processes, resulting in narrower heat-affected zones. On the other hand, most metals are highly reflective when the laser beam impinges perpendicular to the surface, making the process inefficient. Hence, this work proposes to employ shallow angle incidence to reduce the reflectivity during the welding of Ti6Al4V material. To explore the potential of this idea, the current study focuses on studying the effect of laser incident angle (15°-90°), power (300 W-1500 W), and feed rate (10 mm/s-25 mm/s) on autogenous weld bead geometry. For this purpose, bead-on plate (BOP) LBW is conducted on mill-annealed Ti6Al4V material of dimensions 25 mm × 25 mm × 3 mm by employing a fiber laser source with a maximum power of 3 kW and a wavelength of 1080 nm. It is observed from the results that at a normal incident angle and low laser power (< 600 W), the penetration depth is too low to generate a weld bead. Analyzing the cross-section of the weld bead, obtained from SEM, perpendicular to the weld direction reveals that the increase in laser incident angle up to an optimal angle resulted in increased bead dimensions (width and height), and beyond that, the dimensions decreased. However, the optimal incident angle changed when the laser power was changed. The major finding of this study is that at 600 W and a normal incident angle, the laser could not penetrate and generate a weld bead due to low absorptivity, while at an incident angle of 300, 450, and 600, weld beads are generated because of increased absorptivity. Similarly, the increase in weld dimensions with the increase in laser power is observed. At higher laser power, underfill and oxide formation are observed. The feed rate is less predominant than the incident angle and the power.

High-Quality and Enhanced-Resolution Single-Pixel Imaging Based on Spiral Line Array Laser Source

High-Quality and Enhanced-Resolution Single-Pixel Imaging Based on Spiral Line Array Laser Source

Establishing laser cutting of components for sulfide-based solid-state batteries

The demand for safe, power- and energy-dense, low-cost batteries is constantly increasing due to the global shift toward renewable energy sources and the associated need for battery electric vehicles and grid-level energy storage. However, current-generation lithium-ion batteries are struggling to meet the requirements and are reaching their physicochemical limits regarding energy density. Solid-state battery technology promises to improve the current state of the art in electrochemical energy storage and has proven itself in research, although not yet in commercial applications. One of the main challenges in bringing the technology to the market is the limited knowledge and research on the production of solid-state batteries with commercially viable technologies. This study investigates the application of laser cutting technology to improve the cutting process in the production of sulfide-based solid-state batteries. Challenges such as the production atmosphere, handling of the components, and differences compared to conventional battery components are discussed. Using a picosecond laser source, the influence of the pulse frequency, peak fluence, scanning speed, and laser passes was investigated to identify appropriate parameters for cutting sulfide-based composite cathodes. The findings were then successfully applied to the cutting of sulfide-based solid electrolyte separators. An improvement in edge quality compared to mechanical punching is demonstrated, marking a crucial step toward the commercialization of solid-state batteries.

Full-field amplitude speckle decorrelation angiography.

We propose a new simple and cost-effective optical imaging technique, full-field amplitude speckle decorrelation angiography (FASDA), capable of visualizing skin microvasculature with high resolution, and sensitive to small, superficial vessels with slow blood flow and larger, deeper vessels with faster blood flow. FASDA makes use of a laser source with limited temporal coherence, can be implemented with cameras with conventional frame rates, and does not require raster scanning. The proposed imaging technique is based on the simultaneous evaluation of two metrics: the blood flow index, a contrast-based metric used in laser speckle contrast imaging, and the adaptive speckle decorrelation index (ASDI), a new metric that we defined based on the second-order autocorrelation function that considers the limited speckle modulation that occurs in partially-coherent imaging. We demonstrate excellent delineation of small, superficial vessels with slow blood flow in skin nevi using ASDI and larger, deeper vessels with faster blood flow using BFI, providing a powerful new tool for the imaging of microvasculature with significantly lower hardware complexity and cost than other optical imaging techniques.