⇦Chinese Physics Letters, 2023, Vol. 40, No. 11, Article code 114204 Preparation of Bi$_{2}$Te$_{3}$ Based on Saturable Absorption System and Its Application in Fiber Lasers Haoyu Wang (王浩宇), Yue-Jia Xiao (肖悦嘉), Qi Liu (刘齐), Xiao-Wei Xing (邢笑伟), Hu-Jiang Yang (杨胡江), and Wen-Jun Liu (刘文军)* Affiliations State Key Laboratory of Information Photonics and Optical Communications, School of Science, Beijing University of Posts and Telecommunications, Beijing 100876, China Received 18 October 2023; accepted manuscript online 2 November 2023; published online 15 November 2023 *Corresponding author. Email: jungliu@bupt.edu.cn Citation Text: Wang H Y, Xiao Y J, Liu Q et al. 2023 Chin. Phys. Lett. 40 114204    Abstract Fiber laser is a fundamental component of laser systems and is of great significance for development of laser technology. Its pulse output can be divided into $Q$-switched and mode-locked. Achieving ultrashort pulse with narrower pulse duration and higher power is the focus of current research on mode-locked lasers. As an important component of fiber laser systems, saturable absorber (SA) can modulate losses in the optical cavity and generate pulses, enabling the laser system to achieve pulse output under long-term normal operating conditions better. Therefore, expanding the selection range of materials with better saturable absorption properties to improve the quality of pulse output is an important topic in current research. Here, the second generation topological insulator Bi$_{2}$Te$_{3}$ single crystal is prepared, and a ring fiber laser system is built with the Bi$_{2}$Te$_{3}$ SA. The mode-locked pulse with a pulse duration of 288 fs and a signal-to-noise ratio of 80.202 dB is realized. This result verifies that Bi$_{2}$Te$_{3}$, as a member of topological insulator, has good saturable absorption characteristics, and has broad prospects for the application research in lasers.
cpl-40-11-114204-fig1.png
cpl-40-11-114204-fig2.png
cpl-40-11-114204-fig3.png
cpl-40-11-114204-fig4.png
 DOI:10.1088/0256-307X/40/11/114204 © 2023 Chinese Physics Society Article Text Fiber lasers have the advantages of good beam quality, high reliability, and low cost, and are widely used in fields such as optical sensing,[1] laser processing,[2] laser medicine,[3] and materials science.[4] In recent years, ultrashort pulse lasers have attracted a great deal of attentions from scholars in the field of ultrafast optics due to their unique advantages such as narrow output pulse duration.[5-19] The realization of ultrashort pulse lasers can be divided into active mode-locking and passive mode-locking.[20-29] The former periodically modulates the phase or amplitude of the optical field by adding a modulator in the resonant cavity. When increasing the complexity of the resonant cavity and pulse broadening, it is difficult to generate stable ultrashort pulse. However, passive mode-locking technologies, such as nonlinear fiber ring mirror, nonlinear polarization rotation, low-dimensional nanomaterial saturable absorber, can generate ultrashort pulse by using the characteristics of gain material or saturable absorber, which has the advantages of high stability and low cost, and is most widely used in ultrashort pulse lasers.[30-42] Saturable absorber (SA), as a passive mode-locking technology with some advantages, has been studied widely in recent years. How to achieve mode-locking is that the saturation absorption effect causes low intensity laser to be absorbed, while high intensity laser is continuously amplified, resulting in a series of pulses. With the further increase in laser demand towards higher power and shorter pulse duration, the demand for SA materials is also increasing.[9] The unique crystal structure of graphene endows it with properties of ultra-high carrier mobility, ultrafast broadband optical response, high flexibility, etc., making it an effective SA.[10] However, its low absorption rate limits its further application in lasers.[11] Topological insulators (TI) are a kind of nanoscale materials with Dirac cone structure. Their surface states are gapless metal states, so they have a higher modulation depth.[13] In addition, TIs inverse the strong coupling effect between the time symmetric spin orbit interaction and the protected surface state, which makes them have unique optical and photoelectric properties,[14] so they are considered to be the most likely alternative to graphene. Bi$_{2}$Te$_{3}$ belongs to the second generation of TI, which has a hexahedral layered structure, and its thermoelectric properties show obvious anisotropy. Different layers of Bi$_{2}$Te$_{3}$ are connected by Te–Bi covalent bond with high bond energy, which ensures the stability of the sheet structure of the material. The different Fermi velocities of the crystals in different directions give Bi$_{2}$Te$_{3}$ unique advantages.[15] In 2009, Chen et al. investigated the Bi$_{2}$Te$_{3}$, and reported its characteristics. The test results show that the material has obvious characteristics of topological insulator. In addition, Bi$_{2}$Te$_{3}$ is very easy to produce and use in practical applications, not only can it be manufactured through existing mature semiconductor technology, but also its performance can be easily tuned. In 2016, Feng et al. conducted a study on the nonlinear optical properties of Bi$_{2}$Te$_{3}$. The Bi$_{2}$Te$_{3}$ crystal was excited by an 800 nm femtosecond pulse laser, and the nonlinear refractive index of the material reached the order of $10^{-14}$ m$^{2}$/W through theoretical calculations and experimental data fitting. This indicates that Bi$_{2}$Te$_{3}$ has excellent nonlinear optical properties and has broad prospects for applications in nonlinear optical devices. Bi$_{2}$Te$_{3}$ has been widely studied and applied in the field of thermoelectric materials, but research in the fields of nonlinear optics is still rare. Based on the above analysis, in this work, we prepare the Bi$_{2}$Te$_{3}$ single crystal and build a fiber laser based on the Bi$_{2}$Te$_{3}$ SA to achieve pulse output. We analyze the experimental data and compare it with the experimental data of other similar materials to explore the application value of the Bi$_{2}$Te$_{3}$ SA. Preparation of Materials. In this experiment, the Bridgman crystal growth method and mechanical peeling method were used to prepare Bi$_{2}$Te$_{3}$ thin films,[16] and the preparation process is shown in Fig. 1. Firstly, the initial reactants were mixed with high-purity Bi (99.999%, Alfa Aesar) and Te (99.999%, Alfa Aesar) according to the ratio and placed evenly in an ampoule. The ampoule was then heated at 850 ℃ for 48 h, and the material inside the ampoule was melted at high temperature. Then, slowly cool the ampoule, and the material begins to crystallize at the bottom of the ampoule as the temperature decreases. By controlling the cooling rate, high-purity Bi$_{2}$Te$_{3}$ single crystals can be obtained.
cpl-40-11-114204-fig1.png
Fig. 1. Bi$_{2}$Te$_{3}$ thin film preparation process flow.
cpl-40-11-114204-fig2.png
Fig. 2. Characterization of Bi$_{2}$Te$_{3}$ SA: [(a), (b)] AFM image and film thickness of 75 nm Bi$_{2}$Te$_{3}$ SA. [(c), (d)] AFM image and film thickness of 200 nm Bi$_{2}$Te$_{3}$ SA.
After obtaining Bi$_{2}$Te$_{3}$ single crystal, a polydimethylsiloxane (PDMS) film was applied to cover the Bi$_{2}$Te$_{3}$ single crystal, and then the PDMS film was quickly peeled off. Due to the excellent electrostatic adsorption ability and adhesion effect of PDMS, Bi$_{2}$Te$_{3}$ thin films can be obtained by quickly peeling off the PDMS film. The morphology and thickness of Bi$_{2}$Te$_{3}$ thin films can be observed with atomic force microscopy (AFM) shown in Fig. 2. As shown in Fig. 2(b), the randomly selected line from Fig. 2(a) suggests that the thickness is 75 nm. As displayed in Fig. 2(d), the cross-section height profile along the line in Fig. 2(c) indicates the thickness of 200 nm. Then, we made sandwich type saturable absorption devices from the dense and flat Bi$_{2}$Te$_{3}$ thin films for use in laser systems. Experimental Setup. We build an erbium-doped fiber laser system with Bi$_{2}$Te$_{3}$ SA, and the device diagram is shown in Fig. 3. The laser system contains a pump operating at 980 nm, a wavelength division multiplexer (WDM), an erbium doped fiber (EDF), an optical coupler (OC), Bi$_{2}$Te$_{3}$ SA, an isolator (ISO), and a polarization controller (PC), with a ring cavity length of 530.7 cm. The light generated by the pump enters the laser cavity through a 980/1550 nm WDM and is amplified by EDF. We determined its length to be 36 cm based on the pump power. There is 20% of the light that is separated by the OC for observation of the working status and measurement of data. ISO is used to ensure unidirectional transmission of light, prevent reverse transmission of light from damaging optical components in laser systems, and has a certain degree of polarization adjustment ability. PC is used to further regulate the polarization state of light, making the state of the laser more stable. Bi$_{2}$Te$_{3}$ SA can modulate the loss in the optical cavity, which is conducive to achieving narrower pulse duration and higher power pulse output. Finally, using the following equipment, we completed the detailed exploration and characterization of laser: The waveform was observed and recorded by an oscilloscope (Tektronix DPO 3054). The pulse duration was observed and recorded by an autocorrelator (APE Pulse check). The optical spectrum was observed and recorded by a spectrum analyzer (Yoko-gawa AQ 6370 C). The spectrum of the pulse was observed and recorded by a radio frequency (RF) spectrum analyzer (Rohde & Schwarz FSW26).
cpl-40-11-114204-fig3.png
Fig. 3. Device diagram of mode-locked fiber laser.
Experimental Data Analysis. In this experiment, we tested the Bi$_{2}$Te$_{3}$ SA with a thickness of 200 nm. After multiple tests by turning on the pump, it was found that a mode-locked waveform can be obtained when the pump power is 173 mA, with a relatively low threshold. This indicates that the ring fiber laser can easily achieve stable mode-locked pulses, and we can measure its mode-locked pulse waveform through an oscilloscope (Fig. 4). We measured the pulse duration of the laser and fitted the sech$^{2}$ curve to obtain a pulse duration of 288 fs [Fig. 4(a)]. This data result is better compared to other experimental results of Bi$_{2}$Te$_{3}$ SA. Using an RF spectrometer, we obtained that the pulse is concentrated at a repetition frequency of 37.78 MHz, with a signal-to-noise ratio (SNR) of 80.202 dB [Fig. 4(b)]. To further verify the stability of the pulse, we measured the spectrum of the output pulse using a spectral analyzer [Fig. 4(c)]. The central wavelength of the spectrum is stable at 1566.60 nm, with a bandwidth of 25.20 nm. In addition, we recorded the optical spectrum every over 5 h. Especially, the spectral shape, spectral intensity, spectrum bandwidth remained unchanged over this time period, suggesting that the long-term stability is good. We calculated the time bandwidth product (TBP) using the following formula: \begin{align*} {\rm TBP}=c\frac{\Delta \tau \Delta \lambda }{\lambda^{2}}. \end{align*} The TBP is 0.8872, which fully verifies the reliability of the mode-locked pulse output. Based on the above results, we found that the pulse output properties of Bi$_{2}$Te$_{3}$ SA mode-locked fiber laser are good. In order to further verify the value of further research and application prospects of Bi$_{2}$Te$_{3}$ as an SA material, we compare the experimental results in this work with other TI materials or other experimental results of the same material (Table 1).
cpl-40-11-114204-fig4.png
Fig. 4. Output characterization of a 200 nm Bi$_{2}$Te$_{3}$ SA mode-locked fiber laser: (a) pulse duration, (b) peak distribution in the RF spectrum, (c) femtosecond pulse output spectrum, (d) mode-locked pulse sequence.
Table 1. Comparison of pulse output data of TIs SA mode-locked fiber laser.
Materials Pulse width Pulse energy Energy conversion SNR Repetition frequency Mode-locked threshold References
(fs) (nJ) rate(%) (dB) (MHz) (mW)
Sb$_{2}$Te$_{3}$ $1.32 \times 10^{3}$ $283.84 \times 10^{3}$ 0.51 61.21 10.88 307.6 20
Sb$_{2}$Te$_{3}$ 380 $32 \times 10^{-3}$ 0.13 67 17.07 320 21
Sb$_{2}$Te$_{3}$ 128 $44.8 \times 10^{-3}$ 0.3 65 22.32 80 22
Sb$_{2}$Se$_{3}$ 890 4.19 9.36 57 22.36 390 23
Bi$_{2}$Se$_{3}$ $210 \times 10^{3}$ 0.83 5.5 49 32.68 125 24
Bi$_{2}$Se$_{3}$ 579 0.112 1.1 54 14.25 60 25
Bi$_{2}$Se$_{3}$ $398 \times 10^{6}$ 0.527 105 26
Bi$_{2}$Te$_{3}$ $1.63 \times 10^{3}$ 0.259 1.98 80.1 13.5 44.9 27
Bi$_{2}$Te$_{3}$ $230 \times 10^{3}$ 0.599 0.43 77 1.44 200 28
Bi$_{2}$Te$_{3}$ $317 \times 10^{3}$ 2.8 19.8 230 29
Bi$_{2}$Te$_{3}$ 505 67.7 13.14 63.7 30
Bi$_{2}$Te$_{3}$ 288 3.6 80.20 37.78 173 This work
We find from analysis that the pulse duration of the Bi$_{2}$Te$_{3}$ SA mode-locked pulse in this work is narrower, and the SNR, mode-locked threshold and other data also perform well. Compared to Ref. [27], the pulse duration was shortened by one order of magnitude when the SNR was close.[27] Compared to Ref. [30] the SNR was also improved by 18.5% when the pulse duration was shortened by 43%. Overall, although the mode-locked threshold based on the Bi$_{2}$Te$_{3}$ SA fiber laser is slightly higher than that of the Bi$_{2}$Se$_{3}$ SA, it is still at a relatively low level,[20-30] which can be reduced to $ < $ 50 mW.[27] Then we conducted a theoretical analysis on the principle of good output performance of the Bi$_{2}$Te$_{3}$ SA fiber laser. Due to the high nonlinear refractive index of Bi$_{2}$Te$_{3}$, strong self-interaction will occur when the laser passes through the Bi$_{2}$Te$_{3}$ SA, leading to strong nonlinear optical effects in the process of light transmission, such as self-focusing and self-phase modulation. Those nonlinear effects can cause the focusing and bunching of laser beams, thereby increasing the intensity of the light field in a small region, making it easier to achieve laser amplification and photon emission. Therefore, the high nonlinear refractive index of Bi$_{2}$Te$_{3}$ SA results in a shorter transmission distance of light, requiring less laser power or current to reach the mode-locked threshold. The experimental results, combined with Bi$_{2}$Te$_{3}$, have good bandgap (0.15 eV) and carrier concentration ($1.2 \times 10^{-19}$ cm$^{-3}$), which indicates that Bi$_{2}$Te$_{3}$, as a relatively new TI-like SA material, has good saturable absorption characteristics in the near-infrared band, which is conducive to achieving better pulse output. In summary, we have introduced a mode-locked fiber laser based on the Bi$_{2}$Te$_{3}$ SA. Firstly, Bi$_{2}$Te$_{3}$ thin films have been prepared using the Bridgman crystal growth method and mechanical peeling method. Then, an erbium-doped fiber laser has been constructed based on the Bi$_{2}$Te$_{3}$ SA and successfully achieved mode-locked pulse. The pulse duration of this mode-locked pulse can reach 288 fs, with a repetition frequency of 37.79 MHz and an SNR of 80.202 dB. Compared with the experimental results of Bi$_{2}$Te$_{3}$ SA or other TI material SA fiber lasers, the present result has achieved certain optimization and improvement in pulse duration, SNR, mode locking threshold, etc. This work not only measured the nonlinear optical properties of the Bi$_{2}$Te$_{3}$ by combining the TI-material Bi$_{2}$Te$_{3}$ with fiber laser, but also theoretically analyzed the principle of Bi$_{2}$Te$_{3}$-SA mode-locked fiber laser system to achieve good pulse output. From the perspective of nonlinear refractive index, Bi$_{2}$Te$_{3}$ can be used as a good SA material for research and application in fiber lasers. Due to its excellent nonlinear optical properties, combined with its advantages of easy production, preparation, and tuning, Bi$_{2}$Te$_{3}$ can be further studied and developed in combination with fiber lasers, and has good application prospects in the field of nonlinear optics. Acknowledgments. This work was supported by the National Key Research and Development Program of China (Grant No. 2022YFB4601101), the Beijing Natural Science Foundation (Grant No. JQ21019), and the National Natural Science Foundation of China (Grant Nos. 11975001, 12075034, and 12261131495). References Femtosecond laser micromachining in transparent materialsTime-of-flight measurement with femtosecond light pulsesSeveral new directions for ultrafast fiber lasers [Invited]Dispersion engineering of mode-locked fibre lasersTunable all-normal-dispersion femtosecond Yb:fiber laser with biased nonlinear amplifying loop mirrorObservation of 115 GHz high-order harmonic noise-like pulse in Er/Yb-doped fiber laserSwitchable single- and dual-wavelength femtosecond mode-locked Er-doped fiber laser based on carboxyl-functionalized graphene oxide saturable absorberSub-200 fs soliton mode-locked fiber laser based on bismuthene saturable absorberTunable Dual-Wavelength Fiber Laser in a Novel High Entropy van der Waals MaterialGraphene Mode-Locked Ultrafast LaserNanotube and graphene saturable absorbers for fibre lasersA Self-Diffraction Temporal Filter for Contrast Enhancement in Femtosecond Ultra-High Intensity LaserBroadband optical and microwave nonlinear response in topological insulatorUltrasonic-assisted preparation of graphene oxide carboxylic acid polyvinyl alcohol polymer film and studies of thermal stability and surface resistivityElectronic structure of antimonene grown on Sb2Te3 (111) and Bi2Te3 substratesFemtosecond Fiber Laser Based on BiSbTeSe2 Quaternary Material Saturable AbsorberA 66 fs highly stable single wall carbon nanotube mode locked fiber laserMultiband Dynamics of Extended Harmonic Generation in Solids under Ultraviolet InjectionDesign and Development of a High-Performance LED-Side-Pumped Nd:YAG Rod LaserThulium holmium-doped fiber laser mode-locked using Sb2Te3 saturable absorber coated arc-shaped fiberSPIE ProceedingsSub-130 fs mode-locked Er-doped fiber laser based on topological insulatorExperimental demonstration of harmonic mode-locking in Sb2Se3-based thulium-doped fiber laserBi2 Se3 as a saturable absorber for ultrafast photonic applications of Yb-doped fiber lasersBilayer Bismuth Selenide nanoplatelets based saturable absorber for ultra-short pulse generation (Invited)Large-energy mode-locked ytterbium-doped linear-cavity fiber laser based on chemical vapor deposition-Bi2 Se3 as a saturable absorberGeneration of Kelly and dip type sidebands soliton employing Topological insulator (Bi2Te3) as saturable absorberAll-normal-dispersion dissipative-soliton fiber laser at 1.06 µ m using a bulk-structured Bi2 Te3 topological insulator-deposited side-polished fiberYb-doped passively mode-locked fiber laser with Bi2 Te3 -depositedPMMA Sandwiched Bi2 Te3 Layer as a Saturable Absorber in Mode-Locked Fiber LaserFlat Top Optical Frequency Combs Based on a Single-Core Quantum Cascade Laser at Wavelength of ∼ 8.7 μmPassively Q-switched tri-wavelength Yb^3+:GdAl_3(BO_3)_4 solid-state laser with topological insulator Bi_2Te_3 as saturable absorberNonreciprocal Phonon Laser in an Asymmetric Cavity with an Atomic EnsembleMode-Locked YDFL Using Topological Insulator Bismuth Selenide Nanosheets as the Saturable AbsorberWhispering Gallery Mode Lasing Performance’s Evolution of Floating GaN Microdisks Varying with Their ThicknessTunable mode-locked thulium doped fiber laser using manganese phosphorus triselenide (MnPSe3) in 2.0 μmBroadband Sheet Parametric Oscillator for χ(2) Optical Frequency Comb Generation via Cavity Phase Matching635-nm Visible Pr3+ -Doped ZBLAN Fiber Lasers Q-Switched by Topological Insulators SAsOrange-light passively Q-switched Pr^3+-doped all-fiber lasers with transition-metal dichalcogenide saturable absorbersAn All-Fiberized Chirped Pulse Amplification System Based on Chirped Fiber Bragg Grating Stretcher and CompressorFemtosecond harmonic mode-locking of a fiber laser based on a bulk-structured Bi_2Te_3 topological insulatorRed-diode-clad-pumped CW and mode-locked Er:ZBLAN fiber laser at 3.5 µm
[1] Gattass R R and Mazur E 2008 Nat. Photonics 2 219
[2] Lee J, Kim Y J, Lee S, and Kim S W 2010 Nat. Photonics 4 716
[3] Fu W, Wright L G, Backus S, and Frank W 2018 Opt. Express 26 9432
[4] Woodward R I 2018 J. Opt. 20 033002
[5] Song Y Q, Jia X Z, Lin Q M, Yan L, Lu B L, and Bai J T 2021 Appl. Phys. Express 14 102002
[6] Lin Q M, Hou L, He X, Sun J, Lu B L, Chen H W, and Bai J T 2017 Laser Phys. Lett. 14 075102
[7] Lin Q M, Yan L, Jia X Z, and Bai J T 2021 Chin. Opt. Lett. 19 111405
[8] Guo B, Wang S H, Wu Z X, Wang Z X, Wang D H, Huang H, Ge Y Q, and Zhang H 2018 Opt. Express 26 22750
[9] Cui W W, Xing X W, Chen Y Q, Ye H, and Liu W J 2023 Chin. Phys. Lett. 40 024201
[10] Sun Z P, Hasan T, Torrisi F, Popa D, Privitera G, Wang F Q, Basko D M, and Ferrari A C 2010 ACS Nano 4 803
[11] Martinez A and Sun Z P 2013 Nat. Photonics 7 842
[12] Wang X Z, Wang Z H, Wang Y Y, Song J J, and Wei Z Y 2021 Chin. Phys. Lett. 38 074202
[13] Chen S Q, Zhao C J, Li Y, Huang H H, Zhang H, and Wen S C 2014 Opt. Mater. Express 4 587
[14] Li Y S, Li J H, Li Y H, Li Y L, Niu S, and Li N 2018 Ultrason. Sonochem. 40 798
[15] Lei T, Liu C, Zhao J L, Li J M, Li Y P, Wang J O, Wu R, Wang H Q, and Ibrahim K 2016 J. Appl. Phys. 119 015302
[16] Xiao Y J, Xing X W, Cui W W, Zhou Q, and Liu W J 2023 Chin. Phys. Lett. 40 054201
[17] Yu Z H, Wang Y G, Zhang X, Tian J R, and Song Y R 2014 Laser Phys. 24 015105
[18] Lang Y, Peng Z Y, and Zhao Z X 2022 Chin. Phys. Lett. 39 114201
[19] Shen J P, Huang X, Jiang S T, Jiang R R, Wang H Y, Lu P, Jiao M Y 2022 Chin. Phys. Lett. 39 104201
[20] Ahmad H, Yusoff N, and Reduan S A 2022 Infrared Phys. & Technol. 125 104228
[21] Kowalczyk M, Boguslawski J, Stachowiak D, Tarka J, Zybala R, Mars K, Mikula A, Sotor J Z, and Abramski K M 2016 Proc. SPIE 9893 1
[22] Sotor J, Sobon G, and Abramski K M 2014 Opt. Express 22 13244
[23] Ma X H, Chen W, Tong L, Liu S Q, Dai W W, Ye S S, Zheng Z Q, Wang Y Y, Zhou Y, Zhang W, Fang W T, Liao M S, and Gao W Q 2021 Opt. Laser Technol. 143 107286
[24] Li K X, Tian J R, Song Y R, Liu J H, Guoyu H Y, Wang M, and Fang X H 2016 Opt. Eng. 55 036110
[25] Xu Y H, Xie H H, Jiang G B, Miao L L, Wang K, Tang S Y, Zhang H, and Bao Q L 2017 Opt. Commun. 395 55
[26] Han X L, Zhang H N, Zhang C, Li C H, Guo Q X, Gao J J, and Man B Y 2019 Appl. Opt. 58 2695
[27] Haris H, Muhammad A R, Tan S J, Markom A M, Hasnan M M, and Saad I 2022 Infrared Phys. & Technol. 123 104154
[28] Chi C, Koo J, and Lee J H 2014 Laser Phys. 24 105106
[29] Li L, Yan P G, Wang Y G, Sun H, and Si J H 2015 Chin. Phys. B 24 124204
[30] Jiang G B, Zhou Y, Wang L L, and Chen Y 2018 Adv. Condens. Matter Phys. 2018 7578050
[31] Ma Y, Li W J, Xu Y F, Liu J Q, Zhou N, Yang K, Zhang J C, Zhai S Q, Wang L J, and Liu F Q 2023 Chin. Phys. Lett. 40 014201
[32] Sun Y J, Lee C K, Xu J L, Zhu Z J, Wang Y Q, Gao S F, You Z Y, and Tu C Y 2015 Photonics Res. 3 A97
[33] Huang K W, Wang X, Wu L, and Xiong H 2023 Chin. Phys. Lett. 40 104201
[34] Haris H, Batumalay M, Tan S J, Markom A M, Muhammad A R, Hasnan M M, and Saad I 2022 Crystals 12 489
[35] Zhu G Y, Tian M F, Almokhtar M, Qin F F, Li B H, Zhou M Y, Gao F, Yang Y, He S Q, and Wang Y J 2022 Chin. Phys. Lett. 39 123401
[36] Ahmad H, Samion M Z, and Ismail M F 2022 J. Lumin. 252 119348
[37] Ni X, Jia K P, Wang X H, Liu H Y, Guo J, Huang S W, Yao B C, Sernicola N, Wang Z L, Lv X J, Xie Z D, and Zhu S N 2021 Chin. Phys. Lett. 38 064201
[38] Wu D D, Cai Z P, Zhong Y L, Peng J, Weng J, Chen N, and Xu H Y 2015 IEEE Photonics Technol. Lett. 27 2379
[39] Li W S, Peng J, Zhong Y L, Wu D D, Lin H Y, Cheng Y J, Luo Z Q, Xu H Y, and Cai Z P 2016 Opt. Mater. Express 6 2031
[40] Wang M X, Li P X, Xu Y T, Li S, and Yao C F 2022 Chin. Phys. Lett. 39 024201
[41] Lee J, Koo J, Jhon Y M, and Lee J H 2015 Opt. Express 23 6359
[42] Qin Z P, Zhou Y C, Xie G Q, Ma J G, and Qian L J 2022 Opt. Express 30 11174