Lasers and Laser Optics|191 Article(s)
Direct amplification of femtosecond optical vortices in a single-crystal fiber
Changsheng Zheng, Tianyi Du, Lei Zhu, Zhanxin Wang, Kangzhen Tian, Yongguang Zhao, Zhiyong Yang, Haohai Yu, and Valentin Petrov
Spatially twisted light with femtosecond temporal structure is of particular interest in strong-field physics and light–matter interactions. However, present femtosecond vortex sources exhibit limited power handling capabilities, and their amplification remains an ongoing challenge particularly for high-order orbital angular momentum (OAM) states due to several inherent technical difficulties. Here, we exploit a straightforward approach to directly amplify a femtosecond optical vortex (FOV, OAM=-8ℏ) by using a two-stage single-crystal fiber (SCF) amplifier system without pulse stretching and compression in the time domain, delivering 23-W, 163-fs pulses at a repetition rate of 1 MHz. The spatial and temporal features are well-conserved during the amplification, as well as the high modal purity (>96%). The results indicate that the multi-stage SCF amplifier system is particularly suited for direct amplification of high-order FOVs. The generated high-power femtosecond OAM laser beams are expected to help reveal complex physical phenomena in light–matter interactions and pave the way for practical applications in attoscience, laser plasma acceleration, and high-dimension micromachining.
Photonics Research
  • Publication Date: Dec. 14, 2023
  • Vol. 12, Issue 1, 27 (2024)
High-power distributed feedback lasers based on InP corrugated sidewalls at λ∼2 μm|Editors' Pick
Yongqiang Sun, Yunfei Xu, Jinchuan Zhang, Fengmin Chen, Junqi Liu, Shuman Liu, Quanyong Lu, Ning Zhuo, Lijun Wang, Fengqi Liu, and Shenqiang Zhai
We report a high-power single-mode InP-based 2 μm distributed feedback (DFB) laser with a second-order buried grating and corrugated sidewalls. A second-order semiconductor grating is used for in-plane feedback and vertical out-coupling. The corrugated sidewalls are used to eliminate higher-order transverse modes. For the DFB laser with a 2 mm long cavity and 15 μm wide ridge, the maximum continuous-wave edge-emitting and surface-emitting single-mode powers at 300 K are up to 81 and 42 mW, respectively. A single-lobed far-field radiation pattern with a low divergence angle of approximately 8.6° is achieved by a device with a ridge width of 15 μm. The single-longitudinal-mode emission wavelength of the fabricated laser can be adjusted from 2003.8 nm at 288 K to 2006.9 nm at 313 K without any mode hopping. Robust single-mode emission with a side-mode suppression ratio of 30 dB is achieved under all injection currents and temperature conditions.
Photonics Research
  • Publication Date: Jul. 27, 2023
  • Vol. 11, Issue 8, 1390 (2023)
Photonic integrated spiking neuron chip based on a self-pulsating DFB laser with a saturable absorber
Yuechun Shi, Shuiying Xiang, Xingxing Guo, Yahui Zhang, Hongji Wang, Dianzhuang Zheng, Yuna Zhang, Yanan Han, Yong Zhao, Xiaojun Zhu, Xiangfei Chen, Xun Li, and Yue Hao
We proposed and experimentally demonstrated a simple and novel photonic spiking neuron based on a distributed feedback (DFB) laser chip with an intracavity saturable absorber (SA). The DFB laser with an intracavity SA (DFB-SA) contains a gain region and an SA region. The gain region is designed and fabricated by the asymmetric equivalent π-phase shift based on the reconstruction-equivalent-chirp technique. Under properly injected current in the gain region and reversely biased voltage in the SA region, periodic self-pulsation was experimentally observed due to the Q-switching effect. The self-pulsation frequency increases with the increase of the bias current and is within the range of several gigahertz. When the bias current is below the self-pulsation threshold, neuronlike spiking responses appear when external optical stimulus pulses are injected. Experimental results show that the spike threshold, temporal integration, and refractory period can all be observed in the fabricated DFB-SA chip. To numerically verify the experimental findings, a time-dependent coupled-wave equation model was developed, which described the physics processes inside the gain and SA regions. The numerical results agree well with the experimental measurements. We further experimentally demonstrated that the weighted sum output can readily be encoded into the self-pulsation frequency of the DFB-SA neuron. We also benchmarked the handwritten digit classification task with a simple single-layer fully connected neural network. By using the experimentally measured dependence of the self-pulsation frequency on the bias current in the gain region as an activation function, we can achieve a recognition accuracy of 92.2%, which bridges the gap between the continuous valued artificial neural networks and spike-based neuromorphic networks. To the best of our knowledge, this is the first experimental demonstration of a photonic integrated spiking neuron based on a DFB-SA, which shows great potential to realizing large-scale multiwavelength photonic spiking neural network chips.
Photonics Research
  • Publication Date: Jul. 20, 2023
  • Vol. 11, Issue 8, 1382 (2023)
Open-ended exploration of ultrashort pulse lasers: an innovative design strategy for devices based on 2D materials
Qing Wu, Gang Zhao, Haibin Wu, and Meng Zhang
Photonics Research
  • Publication Date: Jun. 23, 2023
  • Vol. 11, Issue 7, 1238 (2023)
Dynamics of a dispersion-tuned swept-fiber laser
Duidui Li, Guolu Yin, Ligang Huang, Lei Gao, Laiyang Dang, Zeheng Zhang, Jingsheng Huang, Huafeng Lu, and Tao Zhu
In this paper, we studied the dynamics of a dispersion-tuned swept-fiber laser both experimentally and theoretically. By adding a dispersion compensation fiber and an electro-optic modulator in the laser cavity, an actively mode-locked laser was obtained by using intensity modulation, and wavelength sweeping was realized by changing the modulation frequency. Using a high-speed real-time oscilloscope, the dynamic behaviors of the swept laser were investigated during wavelength switching, static-sweeping cycle, and continuous sweeping, respectively. It was found that the laser generates relaxation oscillation at the start of the sweeping mode. The relaxation oscillation process lasted for about 0.7 ms, and then the laser started to operate stably. Due to the nonlinear effect, new wavelengths were generated in the relaxation oscillation process, which is not beneficial for applications. Fortunately, relaxation oscillation disappears if the laser starts up and operates in the continuous sweeping mode, and the good sweeping symmetry between the positive sweep and negative sweep increases the application potential of the laser. In addition, the instantaneous linewidth is almost the same as that in the static state. These results describe the characteristics of the laser from a new perspective and reveal, to the best our knowledge, the intensity dynamics of such lasers for the first time. This paper provides some new research basis for understanding the establishment process of dispersion-tuned swept-fiber lasers and their potential application in the future.
Photonics Research
  • Publication Date: May. 19, 2023
  • Vol. 11, Issue 6, 999 (2023)
Hundredfold increase of stimulated Brillouin-scattering bandwidth in whispering-gallery mode resonators|Editors' Pick
Guoping Lin, Jingyi Tian, Tang Sun, Qinghai Song, and Yanne K. Chembo
Backward stimulated Brillouin scattering (SBS) is widely exploited for various applications in optics and optoelectronics. It typically features a narrow gain bandwidth of a few tens of megahertz in fluoride crystals. Here we report a hundredfold increase of SBS bandwidth in whispering-gallery mode resonators. The crystalline orientation results in a large variation of the acoustic phase velocity upon propagation along the periphery, from which a broad Brillouin gain is formed. Over 2.5 GHz wide Brillouin gain profile is theoretically found and experimentally validated. SBS phenomena with Brillouin shift frequencies ranging from 11.73 to 14.47 GHz in ultrahigh QZ-cut magnesium fluoride cavities pumped at the telecommunication wavelength are demonstrated. Furthermore, the Brillouin–Kerr comb in this device is demonstrated. Over 400 comb lines spanning across a spectral window of 120 nm are observed. Our finding paves a new way for tailoring and harnessing the Brillouin gain in crystals.
Photonics Research
  • Publication Date: May. 16, 2023
  • Vol. 11, Issue 6, 917 (2023)
Widely tunable continuous-wave visible and mid-infrared light generation based on a dual-wavelength switchable and tunable random Raman fiber laser|Editors' Pick
Han Wu, Weizhe Wang, Bo Hu, Yang Li, Kan Tian, Rui Ma, Chunxiao Li, Jun Liu, Jiyong Yao, and Houkun Liang
Nonlinear frequency conversion of wavelength agile and high-power random fiber lasers can provide a promising way to generate continuous-wave (CW) visible and mid-infrared (MIR) light with unique properties such as the continuous modeless spectrum, low temporal/spatial coherence, and high temporal stability. Here, we report a dual-wavelength switchable and tunable random Raman fiber laser (RRFL) based on a phosphosilicate fiber that has two Raman gain peaks for the first time and demonstrate its superior capability to generate widely tunable CW visible and mid-infrared light via nonlinear frequency conversions. By using the combination of a tunable pump and two tunable gratings in Littrow configuration that can provide separated point feedback for the two Stokes wavelengths corresponding to silica- and phosphorus-related Raman peaks, the spectrum of an RRFL can be flexibly manipulated for the aim of nonlinear frequency conversions, including single-wavelength tunable emission at the 1.1 μm or 1.2 μm band for second-harmonic generation (SHG), dual-wavelength simultaneously tunable emission at the 1.1 μm and 1.2 μm bands for the sum-frequency generation (SFG), and dual-wavelength separation tunable emission for difference-frequency generation (DFG). As a result, with the combination of SHG and SFG in a periodically poled lithium niobate crystal array, we experimentally demonstrate the broadest tuning range (560–630 nm) of visible light generated from an RRFL, to the best of our knowledge. The tunable MIR light in the range of 10.7–12.3 μm is also demonstrated through DFG of an RRFL operating in separation tunable dual-wavelength emission mode in a BaGa4Se7 (BGSe) crystal, which is the first realization of >10 μm CW DFG in the BGSe crystal. We believe the developed dual-wavelength switchable and tunable RRFL can provide a new compact, robust, and cost-effective platform to realize broadly tunable light in both the visible and MIR regions, which can also find potential applications in imaging, sensing, and temporal ghost imaging in various spectral bands.
Photonics Research
  • Publication Date: May. 01, 2023
  • Vol. 11, Issue 5, 808 (2023)
Direct generation of 3.17 mJ green pulses in a cavity-dumped Ho3+-doped fiber laser at 543 nm|Editors' Pick
Tianran Li, Ziyu Wang, Jinhai Zou, Jinfen Hong, Qiujun Ruan, Hang Wang, Zhipeng Dong, and Zhengqian Luo
High-energy pulsed lasers in the green spectral region are of tremendous interest for applications in space laser ranging, underwater detection, precise processing, and scientific research. Semiconductor pulsed lasers currently are difficult to access to the so-called “green gap,” and high-energy green pulsed lasers still heavily rely on the nonlinear frequency conversion of near-IR lasers, precluding compact and low-cost green laser systems. Here, we address this challenge by demonstrating, for the first time to the best of our knowledge, millijoule-level green pulses generated directly from a fiber laser. The green pulsed fiber laser consists of a 450 nm pump laser diode, a Ho3+-doped ZBLAN fiber, and a cavity-dumping module based on a visible wavelength acousto-optic modulator. Stable pulse operation in the cavity-dumping regime at 543 nm is observed with a tunable repetition rate in a large range of 100 Hz–3 MHz and a pulse duration of 72–116 ns. The maximum pulse energy of 3.17 mJ at 100 Hz is successfully achieved, which is three orders of magnitude higher than those of the rare-earth-doped fiber green lasers previously reported. This work provides a model for compact, high-efficiency, and high-energy visible fiber pulsed lasers.
Photonics Research
  • Publication Date: Feb. 27, 2023
  • Vol. 11, Issue 3, 413 (2023)
Controlled generation of picosecond-pulsed higher-order Poincaré sphere beams from an ytterbium-doped multicore fiber amplifier
Kunhao Ji, Di Lin, Ian A. Davidson, Siyi Wang, Joel Carpenter, Yoshimichi Amma, Yongmin Jung, Massimiliano Guasoni, and David J. Richardson
Higher-order Poincaré sphere (HOPS) beams with spatially variable polarization and phase distributions are opening up a host of unique applications in areas ranging from optical communication to microscopy. However, the flexible generation of these beams with high peak power from compact laser systems remains a challenge. Here, we demonstrate the controlled generation of HOPS beams based on coherent beam combination from an Yb-doped multicore fiber (MCF) amplifier. Using a spatial light modulator to adaptively adjust the wavefront and polarization of the signals seeded into the individual cores of the MCF various structured beams (including cylindrical vector beams and first- and second-order vortex beams) were generated with peak powers up to 14 kW for ∼92 ps pulses.
Photonics Research
  • Publication Date: Jan. 23, 2023
  • Vol. 11, Issue 2, 181 (2023)
Self-synchronized temporal-spectral characterization system for revealing ultrafast fiber laser dynamics
Yulong Cao, Zhenghu Chang, Qiang Wu, Jingsheng Huang, Laiyang Dang, Ai Liu, Yiyang Luo, Ligang Huang, Wei Huang, Lei Gao, and Tao Zhu
Due to the electronic bottleneck limited real-time measurement speed of common temporal-spectral detection and the particle-like nature of optical soliton enabled nonrepeatable transient behaviors, capturing the ultrafast laser pulses with unknown times of arrival and synchronously characterizing their temporal-spectral dynamic evolution is still a challenge. Here, using the Raman soliton frequency shift based temporal magnifier and dispersive Fourier transform based spectral analyzer, we demonstrate a self-synchronized, ultrafast temporal-spectral characterization system with a resolution of 160 fs and 0.05 nm, and a recording length above milliseconds. The synchronized nonlinear process makes it possible to image full-filled temporal sub-picosecond pulse trains regardless of their arrival times and without extra pump lasers and photoelectric conversion devices. To demonstrate the significance of this improvement, a buildup dynamic process of a soliton laser with a complex breakup and collisions of multisolitons is visually displayed in the spectral and temporal domains. The soliton dynamic evolution processes observed by our characterization system are in one-to-one correspondence with the numerical simulation results. We believe this work provides a new multidimensional technique to break the electronic bottleneck to gain additional insight into the dynamics of ultrafast lasers and nonlinear science.
Photonics Research
  • Publication Date: Jan. 23, 2023
  • Vol. 11, Issue 2, 173 (2023)
Topics