Single Crystal Fibers Research Articles

The Growth and Spectroscopic Properties of Er, Nd: YSGG Single Crystal Fibers

Single crystal fiber (SCF) is a novel solid gain medium and technique which combines the advantages of glass fiber and single crystal, showing great potential in the field of high-power lasers. In this paper, Er, Nd: YSGG single crystals with diameters of 2 mm and lengths of 80 mm were successfully grown using the micro-pulling-down method for the first time. Then, the measurements of Laue spots and Er3+ distribution indicated that the as-grown crystals were of a high quality. The effect of co-doped Nd3+ on the Er: YSGG was systematically discussed, which demonstrated that Nd3+ can decrease the fluorescence lifetime of Er: 4I13/2 that solve the self-termination bottleneck accordingly. These results demonstrate that Er, Nd: YSGG SCFs are promising materials for the further 3 μm laser generations.

Optical temperature sensing characteristics of Yb3+/Nd3+ co-doped YAG single crystal fiber based on up-conversion luminescence

YAG: 5 mol%Yb3+/x mol%Nd3+(x = 0, 0.5, 1, 2, 4, 7) and YAG: 2 mol%Nd3+ single crystal (SC) fluorescent materials were prepared using laser heated pedestal growth (LHPG) method. The up-conversion (UC) spectra of YAG: Yb3+/Nd3+ were recorded under 980 nm laser excitation, the results show that the optimal material was obtained at 5 mol%Yb3+/2 mol%Nd3+. An integrated YAG single crystal fiber (SCF) with end 5 mol%Yb3+/2 mol%Nd3+ co-doped was prepared by the LHPG method, the temperature-dependent characteristics were measured in the range from 348 K to 1448 K. It shows that the fluorescence intensity increases and then decreases with the increase of temperature. Fluorescence intensity ratios (FIR) in Nd3+ UC spectra, including FIR1 (4F7/2/4F5/2 → 4I9/2), FIR2 (4F9/2/4F5/2 → 4I9/2) and FIR3 (4G5/2/4F9/2 → 4I9/2), vary monotonically in temperature ranges of 348–1273 K, 523–1273 K, and 673–1273 K, respectively. The maximally absolute and relative sensitivities for FIR1 were, respectively, achieved to be 2.34 × 10−3 K−1 at 738 K and 4.61 × 10−1 %K−1 at 390 K, and these values for FIR2 were accordingly achieved to be 1.19 × 10−3 K−1 at 1273 K and 4.59 × 10−1 %K−1 at 735 K, and for FIR3 they were 4.66 × 10−3 K−1 at 1273 K and 4.09 × 10−1 %K−1 at 760 K. Therefore, we believe that the fabricated YAG: Yb3+/Nd3+ fluorescent materials have favorable application potential for optical thermometer.

396 MHz CPA femtosecond laser system based on a single crystal fiber rod-type amplifier

The paper presents the results of multiplying the repetition frequency of the seed source to 396 MHz using an extra-cavity fiber multiplication method. The single crystal fiber rod-type amplifier was able to boost the average output power to approximately 15.9 W. Using a transmission gratings-based pulse compressor, an average output power of 9.56 W was achieved, corresponding to a burst energy of up to 382 µJ and a compression efficiency of 81.7%. The shortest pulse duration was optimized to be 594 fs; however, an obvious pedestal was also observed. This system reduces the impact of nonlinear effects on the device by increasing the repetition frequency, thereby increasing the injection energy of a single process in industrial processing.

Directional and lattice engineering growth of sapphire fibers for ultrasonic ultra-high-temperature sensors

High-temperature sensors for extreme environments are in urgent demand with the rapid development of aerospace, nuclear energy, and advanced manufacturing. Ultrasonic temperature sensors (UTS) are widely used in high-temperature sensing due to their high working temperature that approaches the melting point of the acoustic waveguide. Al2O3 single-crystal fiber (SCF), also called sapphire fiber, is a promising candidate for ultrasonic thermometry due to its ultra-high melting point (∼2050 °C), high strength and oxidation resistance. Here, we report for the first time, to the best of our knowledge, large length-diameter ratio sapphire fibers with specific orientations (a-axis, m-axis, and c-axis) have been grown by laser-heated pedestal growth method and applied for ultrasonic temperature sensing. Sapphire fibers exhibit significant acoustic anisotropy, and a-oriented sapphire fiber has a lower acoustic velocity and a greater velocity-temperature variation, leading to higher sensitivity. Moreover, the acoustic velocity of sapphire fiber could be further decreased by doping with Cr ions owing to the enhanced lattice disorder and crystal density. As a result, an improved unit sensitivity of 28.98–52.88 ns°C−1m−1 and a superior resolution of 1.73–0.95 °C have been achieved in the range of 20–1200 °C via a-oriented Cr:Al2O3 SCF-UTS. More importantly, the sensor performance is positively correlated with ambient temperature, accompanied with the high working temperature (∼1800 °C) and excellent stability (∼20 h), demonstrating promising prospects for applications in high-temperature thermometry. This work provides a feasible approach for designing a high-performance UTS based on acoustic anisotropy and lattice engineering.

The influence of Pr3+ ions on the emission characteristics of Er3+-doped YSGG single crystal fibers in the 1–3 μm wavelength range

A series of 20 mol% Er3+, x mol% Pr3+: Y2.4-3xSc2Ga3O12 (Er3+, Pr3+: YSGG) single-crystal fibers (SCFs) were successfully grown by micro-pulling-down (μ-PD) method. Er3+, Pr3+: YSGG SCFs with varying concentrations of Pr3+ dopant exhibit consistent retention of the identical cubic structural space group. Under 980 nm laser diode (LD) pumping, Er3+, Pr3+: YSGG exhibits two emission bands centered at 1.6 and 2.7 μm, respectively. The incorporation of Pr3+ ions in Er3+, Pr3+: YSGG SCF materials has a negative impact on the emission peak intensity at 1.6 μm within a specific range of doping concentration, while it can relatively enhance the emission peak intensity at 2.7 μm. The lifetime of Er3+ ions at 4I13/2 is showing a significant decrease trend with increasing Pr3+ ions doping concentration. The results presented above indicate that the incorporation of Pr3+ ions increase the likelihood of particle number inversion, improving laser operation and demonstrating the desensitizing influence of Pr3+ ions. Quantitative analysis of the gain cross-section reveals a particle number inversion rate of 52.73% at approximately 2.7 μm. These findings provide valuable insights for developing applications aiming to achieve efficient and precise emission at 2.7 μm using Erbium–Praseodymium co-doped yttrium scandium gallium garnet single crystal fibers.

Light response uniformity of LuAG:Ce scintillating single crystal fiber grown by laser heated pedestal growth method

Own to its fine granularity and sub-millimeter position information, scintillating single crystal fibers (SSCFs) hold great potential for various applications such as electromagnetic calorimeters, positron emission tomography, and radiotherapy dosimetry. The light response uniformity of scintillating fibers is an important parameter for precise measurements of ionizing radiation. Three methods were designed to investigate the light response uniformity of the 184-mm-long LuAG:Ce SCCF. Relatively longitudinal-distributed uniformity of cerium element was obtained in this SSCF. The scintillation light attenuation coefficient of the SSCF is 0.27 cm−1 induced by X-ray photons with single-end readout mode and about 0.29 cm−1 induced by gamma rays with dual-end readout mode. The Ce3+ ions self-absorption along the longitudinal light propagation process is one of main reasons for the scintillation light attenuation. Weakening the Ce3+ ions’ self-absorption effect is a possible way to improve the light response uniformity of the LuAG:Ce SSCF.

Growth, spectroscopy properties and laser operation of a novel single crystal fiber: Nd3+-doped CaY0.9Gd0.1AlO4

A Nd3+-doped CaY0.9Gd0.1AlO4 single crystal fiber (Nd: CYGA SCF) with a length of 80 mm and a diameter of 1 mm, to the best of our knowledge, was successfully grown for the first time by a highly efficient laser-heated pedestal growth method. The basic physical and chemical properties, optical properties, and laser properties of the as-grown SCF were studied in detail. The results show that the Nd: CYGA SCF has wider absorption and emission half-peak full width compared with a bulk single crystal. Furthermore, under the pumping of a commercial 808 nm laser diode, a CW laser operation at 1080 nm with a half-height width of 0.29 nm was obtained. The laser output power was 54 mW at an absorbed power of 2.03 W. The slope efficiency was 6.79% with respect to the absorbed pump power. Thus, the Nd: CYGA SCF might be a practical and powerful candidate for laser gain medium, and have a great research space in the field of lasers.

Watt-level and near diffraction-limited Pr3+-doped single-crystal fiber lasers.

Using a CZ-grown a-cut Pr:YLF crystal as laser gain medium after processing it into crystal fiber, we have demonstrated real Pr3+-doped single-crystal fiber lasers for the first time to the best of our knowledge. This Pr3+ crystal fiber has absorbed up to 20.4 W of pump power, which is the highest absorbed power among Pr3+ lasers. For two representative laser emissions at about 639 nm and 607 nm, we have achieved maximum output powers of 5.45 W and 3.04 W, respectively. Output powers of the two lasers show very good linearities, which indicate that the present output powers are only limited by the available pump power. Both laser emissions have exhibited near diffraction-limited beam qualities. This proposal has provided a good and feasible route for the development of compact, high-power, and high-brightness all-solid-state Pr3+ visible lasers via crystal fiber.

High-efficiency Ho:YAG single-crystal fiber laser in-band pumped by a 1.9 μm laser diode

We report on a 10-watt-level, efficient 2 μm Ho:YAG (0.6 at.% Ho3+ doped Y3Al5O12) single crystal fiber (SCF) laser in-band pumped by a 1.9 μm laser diode. Benefiting from the high gain of the SCF and the unique propagation features of the pump and laser beams, a maximum output power of 10.77 W is achieved with T OC = 20%, corresponding to a slope efficiency of 61.8%. The higher efficiency of 64.8% and the output power of 9.8 W are obtained with T OC = 50%. Compared to the traditional bulk crystal, wave-guiding of the pump light in the SCF can extend the gain region and thus improve the laser efficiency, which provides a simple and effective method to improve the utilization rate of the pump light even for the low-brightness laser diodes.

Oxygen sensing with SrTi1−xFexO3-δ thin films on sapphire optical fiber at extreme temperatures

Optical fiber-based sensors are uniquely suited for in-situ sensing applications that involve high operational temperature and harsh chemical conditions, such as solid oxide fuel cell (SOFC) monitoring, chemical manufacturing, and power generation. Single crystal optical fiber, such as α-alumina (sapphire), provides a substrate that exhibits improved stability over off-the-shelf silica fiber at temperatures above 800 °C. In this work, single crystal sapphire fiber is paired with a high-temperature stable perovskite oxide sensing layer, SrTi0.65Fe0.35FeO3-δ (STF35), to demonstrate all-optical oxygen sensing from 0.01 to 0.19 atm at extreme temperatures (800–1000 °C). The defect chemistry associated with the optical oxygen sensing response is also considered within the context of the current literature and modeled under relevant sensor conditions. Stability is evaluated under dry and humid conditions, and low cross-sensitivity with CO2 is demonstrated, indicating viability for operation on the cathode stream within an operational SOFC or within a post-combustion environment.

Ultra-high melting point Ho3+, Yb3+ co-doped HfO2 single-crystal fibers for high-precision and robust ratiometric thermometry towards harsh environments

Ultra-high melting point Ho3+, Yb3+ co-doped HfO2 single-crystal fibers for high-precision and robust ratiometric thermometry towards harsh environments

Performance analysis of photonic crystal fiber structure based on different highly nonlinear materials

Generally, fiber with a large mode area is desired for fiber laser and beam delivery applications. But the use of these fiber types is restricted to linear optical applications due to the lower value of the nonlinear coefficient. This paper investigates a single material-based photonic crystal fiber (PCF) with improved optical characteristics, applicable for linear and nonlinear optics. The light propagation in the structure is explored by applying finite element solver-based COMSOL multiphysics software. Five nonlinear optical materials are utilized as background material to get the optimized material with high performance PCF. Using this PCF, the improved optical properties of PCF such as moderate effective mode area of 115.85 [Formula: see text], chromatic dispersion, confinement loss of 10[Formula: see text] dB/m, the nonlinear coefficient of 543W[Formula: see text]Km[Formula: see text], splicing loss of 2.013 dB, and numerical aperture are numerically analyzed. This single-mode PCF also shows the low bending loss for the bending radius of 7[Formula: see text]mm. The amended PCF structure is found to be suitable for high-power fiber laser, supercontinuum generation, wavelength conversion, and slow-light generation.

Graphene oxide saturable absorber for a [formula omitted] passively Q-switched single crystal fiber pulsed laser

In this work, the graphene oxide (GO) samples of different oxidation degree prepared by modified Hummers method were drop-coated on sapphire substrates as saturable absorber (SA). On this basis, this work innovatively combines GO, the excellent SA, with single crystal fiber (SCF), the outstanding laser gain medium, for the first time to achieve 1.03μm passively Q-switched pulsed laser output with the maximum average power of 2.183 W and the repetition frequency of 317.42 kHz, which is, to our knowledge, the largest average power of passively Q-switched SCF pulsed laser output reported so far.

Growth and spectroscopic properties investigation of Er:LuYAG and Er/Eu:LuYAG single crystal fibers used in mid-infrared lasers

Growth and spectroscopic properties investigation of Er:LuYAG and Er/Eu:LuYAG single crystal fibers used in mid-infrared lasers

Hundred watt level and high energy compact hybrid fiber femtosecond laser with good beam quality

A hundred watt level compact femtosecond laser system comprised of a high gain, low nonlinearity silicate glass fiber amplifier and a highly efficient Yb:YAG single-crystal fiber amplifier is demonstrated. By reducing the harmful thermal lens effect of amplifiers and optical elements, and precisely tuning dispersion of the stretcher, 110 W, 495 fs laser output at 1 MHz repetition rate and 250 μJ, 494 fs laser output at 200 kHz repetition rate are obtained. An optimized beam-quality factor (M 2) of better than 1.3 is obtained by filtering the beam with a small-aperture diaphragm. To our best knowledge, this is the first demonstration of such a hybrid femtosecond laser over 100 W and 100 μJ with good beam quality.

Temperature dependence of Cr:CYA effective emission cross-section

A high-quality Cr:CYA (Cr:CaYAlO4) single crystal fiber was grown by μ-PD (Micro-Pulling-Down) method. The E//a and E//c polarized excitation spectra of Cr:CYA at room temperature was measured. The crystal field parameters were calculated and the energy level structure of Cr:CYA was analyzed. We also measured the polarization emission spectra and lifetimes at different temperatures and calculated the effective emission cross-section. Based on the above data and Boltzmann law, the thermal distribution between the excited energy levels 2E and 4A2 at different temperatures was analyzed. The present work may be useful for guiding laser research on Cr:CYA and other Cr3+-doped laser crystals above room temperature.

Ultra-wideband and coherent supercontinuum generation (near and mid-infrared) in dispersion flattened ZnGeP2 photonic crystal fiber

Transmission window is a major concern in selecting the background material of photonic crystal fiber for supercontinuum generation. In this work, Zinc-Germanium Diphosphide (ZnGeP2) based single material photonic crystal fiber has been proposed with high nonlinearity and low confinement loss for near and mid-infrared supercontinuum generation. As single material is used, hence the concerned difficulties for choosing separate materials for core and cladding is eliminated. Again, the light transmission window of ZnGeP2 is very large (700 nm – 13000 nm). Optical properties like dispersion, numerical aperture, effective area, nonlinearity and confinement loss are analyzed and demonstrated for a wavelength range of 1000 – 5000 nm. COMSOL software is used to design the fiber and finite element method (FEM) is adopted for numerical analysis. The proposed fiber presents low and flattened dispersion in the range of 2250 – 5000 nm, nonlinearity of the order of 104 W–1km−1 and confinement loss of the order of 10–9 dB/m. The fiber is then used for supercontinuum generation in both near and mid-infrared range and an unprecedented bandwidth of 31000 nm has been achieved which may be pragmatic for outstanding medical applications.

Thermally robust and highly stable method for splicing silica glass fiber to crystalline sapphire fiber.

This research reports an advancement in splicing silica glass fiber to sapphire single-crystal optical fiber (SCF) using a specialized glass processing device, including data that demonstrate the thermal stability of the splice to 1000°C. A filament heating process was used to produce a robust splice between the dissimilar fibers. A femtosecond laser is used to inscribe a fiber Bragg gratings sensor into the SCF to measure the high-temperature capabilities and signal attenuation characteristics of the splice joint. The experimental results demonstrate that the proposed splicing method produces a splice joint that is robust, stable, repeatable, and withstands temperatures up to 1000°C with a low attenuation of 0.5dB. The proposed method allows placement of SCF-based sensors in the extreme environments encountered in various engineering fields, such as nuclear, chemical, aviation, and metals manufacturing, to enable improvements in process monitoring, product quality, and production efficiency.

High-speed and high-resolution YAG fiber based distributed high temperature sensing system empowered by a 2D image restoration algorithm.

High temperature monitoring is critical to the health and performance of vital pieces of infrastructure such as jet engine, fuel cells, coal gasifiers, and nuclear reactor core. However, it remains a big challenge to realize reliable distributed high temperature sensing system with high speed, high spatial and temperature resolution simultaneously. In this work, a Raman distributed high temperature sensing system with high temperature resolution and high spatial resolution was realized in a single-crystal YAG fiber. The sensing system demonstrated operation from room temperature up to 1400°C with a spatial resolution of 7 cm and response time of 1 millisecond in a 1m long YAG fiber. The average temperature sensitivity of the system is about 7.95 × 10-4/°C. To the best of our knowledge, this is the best spatial resolution and response time reported in literature. In this system, a 2D image restoration was used to boost the signal to noise ratio of sensor. Empowered by the algorithm, the average temperature standard deviation along the sensing fiber of 7.89 °C was obtained based on a single frame data in 1 millisecond. A new record of temperature resolution of 0.62 °C was demonstrated in only 1 second frame data traces, which enables a fast response capacity.

Passively Q-switched single crystal fiber pulsed laser at 1.05 µm with T3C2Tx as the saturable absorber.

In this paper, Ti3C2Tx MXene prepared by LiF/HCl etching method was spin-coated on glass substrate and sapphire substrate as the saturable absorber (SA), and the MXene SA is combined with Yb: LuAG single crystal fiber (SCF) for the first time to achieve a 1.05 µm passively Q-switched pulsed laser output with the average power, pulse width, and repetition frequency of 1.989 W, 149.6 ns, and 365.44 kHz, respectively, which is the highest average power ever reported for passively Q-switched SCF pulsed lasers. This work enriches the research on SCF pulsed lasers and provides a feasible approach for achieving high-power all-solid-state pulsed lasers.