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Lasers and Laser Optics|212 Article(s)
Self-injection locked laser via a hollow-core fiber Fabry–Perot resonator
Zitong Feng, Meng Ding, Mateˇj Komanec, Stanislav Zvánovec, Ailing Zhong, Francesco Poletti, Giuseppe Marra, and Radan Slavík
In a hollow-core fiber (HCF), light propagates through an air/vacuum core rather than a solid material, resulting in a low thermo-optic coefficient and ability to handle high powers. Here, we demonstrate a laser locked to a hollow-core fiber reference, which thanks to the low HCF thermal sensitivity, shows long-term stability an order of magnitude better than compact commercially available low-noise lasers. The laser frequency variation within ±600 kHz was measured over 50 h. The stability of our proof-of-concept laser is ensured via a strong self-injection ratio of -15 dB, enabled by the high-power handling and low loss of the hollow-core fiber’s resonator. Moreover, our results show appealing performance parameters, including a fractional frequency stability of 4×10-13 at 1 s averaging time and a Lorentzian component of the linewidth of 0.2 Hz. In a hollow-core fiber (HCF), light propagates through an air/vacuum core rather than a solid material, resulting in a low thermo-optic coefficient and ability to handle high powers. Here, we demonstrate a laser locked to a hollow-core fiber reference, which thanks to the low HCF thermal sensitivity, shows long-term stability an order of magnitude better than compact commercially available low-noise lasers. The laser frequency variation within ±600 kHz was measured over 50 h. The stability of our proof-of-concept laser is ensured via a strong self-injection ratio of -15 dB, enabled by the high-power handling and low loss of the hollow-core fiber’s resonator. Moreover, our results show appealing performance parameters, including a fractional frequency stability of 4×10-13 at 1 s averaging time and a Lorentzian component of the linewidth of 0.2 Hz.
Photonics Research
- Publication Date: Feb. 24, 2025
- Vol. 13, Issue 3, 611 (2025)
Dispersion step tuning fiber laser based on a Mach–Zehnder interferometer
Duidui Li, Guolu Yin, Lei Gao, Ligang Huang, Huafeng Lu, and Tao Zhu
This paper presents a wavelength-stepped swept laser based on a dispersion-tuned swept laser with the integration of a Mach–Zehnder interferometer, enabling a transition from continuous wavelength sweeping to wavelength-stepped sweeping. A comprehensive investigation of this laser is conducted, wherein different modulation schemes are employed to dynamically compare the switching mode, static-sweeping mode, and sweeping mode; the absence of mode hopping in the sweeping mode of the laser is verified. However, it is observed during experiments that the wavelength always remains stationary for a long time during the initiation of sweeping and change in sweeping direction, exhibiting latency compared to the modulation frequency variations. Through a simplistic modeling analysis of the composite cavity, it is revealed that the detuned state of the sub-cavity plays a critical role in the stable operation of the laser. Subsequently, simulation verification using the Ginzburg–Landau equation supports this observation. Additionally, compared to dispersion-tuned swept lasers, not only the linewidth significantly is narrowed in the proposed laser, but it also demonstrates enhanced stability during the sweeping process. This study provides, to our knowledge, a new laser source for ultra-fast optical imaging, ranging, and sensing applications, and presents novel methods and theoretical models for linewidth compression in swept lasers. This paper presents a wavelength-stepped swept laser based on a dispersion-tuned swept laser with the integration of a Mach–Zehnder interferometer, enabling a transition from continuous wavelength sweeping to wavelength-stepped sweeping. A comprehensive investigation of this laser is conducted, wherein different modulation schemes are employed to dynamically compare the switching mode, static-sweeping mode, and sweeping mode; the absence of mode hopping in the sweeping mode of the laser is verified. However, it is observed during experiments that the wavelength always remains stationary for a long time during the initiation of sweeping and change in sweeping direction, exhibiting latency compared to the modulation frequency variations. Through a simplistic modeling analysis of the composite cavity, it is revealed that the detuned state of the sub-cavity plays a critical role in the stable operation of the laser. Subsequently, simulation verification using the Ginzburg–Landau equation supports this observation. Additionally, compared to dispersion-tuned swept lasers, not only the linewidth significantly is narrowed in the proposed laser, but it also demonstrates enhanced stability during the sweeping process. This study provides, to our knowledge, a new laser source for ultra-fast optical imaging, ranging, and sensing applications, and presents novel methods and theoretical models for linewidth compression in swept lasers.
Photonics Research
- Publication Date: Feb. 18, 2025
- Vol. 13, Issue 3, 604 (2025)
Modulation-free laser frequency locking using Fano resonance in a crystalline whispering-gallery-mode cavity
Yingjie Lu, Haotian Wang, Jun Guo, Yaohui Xu, Yuanchen Hu, Wujun Li, Jianing Zhang, Jie Ma, and Deyuan Shen
A low-thermal-noise, small-sized, monolithic crystalline whispering-gallery-mode cavity can achieve a compact laser frequency locking system. In this study, we propose generating a Fano resonance spectrum within the crystalline cavity to achieve frequency locking without the need for traditional modulation techniques, aiming to further simplify the locking system. By coupling a prism with the crystalline cavity, we generate a Fano transmission spectrum to serve as the error signal for laser frequency locking. Experimental results show that our method achieves a level of noise suppression comparable to the classical Pound-Drever-Hall technique, reducing laser frequency noise to near the thermal noise limit of the crystalline cavity. It enables us to suppress the laser frequency noise to below 1 Hz2/Hz in the offset frequency range of 103–105 Hz and achieve a minimum noise of 0.2 Hz2/Hz. We also analyzed various unique optical noises in the Fano locking technique and found that the primary factor limiting laser frequency noise in this work is still the inherent thermal noise of the crystalline cavity. Our results indicate that the proposed Fano locking technique has significant potential to simplify laser locking systems, enhance stability, and reduce overall power consumption and cost. A low-thermal-noise, small-sized, monolithic crystalline whispering-gallery-mode cavity can achieve a compact laser frequency locking system. In this study, we propose generating a Fano resonance spectrum within the crystalline cavity to achieve frequency locking without the need for traditional modulation techniques, aiming to further simplify the locking system. By coupling a prism with the crystalline cavity, we generate a Fano transmission spectrum to serve as the error signal for laser frequency locking. Experimental results show that our method achieves a level of noise suppression comparable to the classical Pound-Drever-Hall technique, reducing laser frequency noise to near the thermal noise limit of the crystalline cavity. It enables us to suppress the laser frequency noise to below 1 Hz2/Hz in the offset frequency range of 103–105 Hz and achieve a minimum noise of 0.2 Hz2/Hz. We also analyzed various unique optical noises in the Fano locking technique and found that the primary factor limiting laser frequency noise in this work is still the inherent thermal noise of the crystalline cavity. Our results indicate that the proposed Fano locking technique has significant potential to simplify laser locking systems, enhance stability, and reduce overall power consumption and cost.
Photonics Research
- Publication Date: Jan. 30, 2025
- Vol. 13, Issue 2, 417 (2025)
Ultra-linear FMCW laser based on time-frequency self-injection locking|Editors' Pick
Jichen Zhang, Shangyuan Li, Xiaoping Zheng, and Xiaoxiao Xue
Frequency-modulated continuous-wave (FMCW) light sources are essential components for coherent light detection and ranging (LiDAR), which is ubiquitously utilized in autonomous driving, industrial monitoring, and geological remote sensing. Traditional FMCW LiDAR systems often face challenges in achieving high frequency-sweep linearity and large excursion, which are critical for accurate distance and velocity measurements. Here, we propose a self-injection locked laser with frequency-shifted feedback to generate ultra-linear and wideband FMCW light. A record-low relative frequency nonlinearity of 6.4×10-7 is achieved when the frequency excursion is 100 GHz and the repetition frequency is 1 kHz. In the LiDAR test, a range resolution of 1.6 mm and a velocity accuracy of 3 mm/s at 300 m distance are demonstrated, and those of 8.1 mm and 6 mm/s at 1 km distance are also obtained. The reported FMCW light source provides not only enhanced performance in coherent LiDAR, but also utilization potential in various high-precision measurement scenarios. Frequency-modulated continuous-wave (FMCW) light sources are essential components for coherent light detection and ranging (LiDAR), which is ubiquitously utilized in autonomous driving, industrial monitoring, and geological remote sensing. Traditional FMCW LiDAR systems often face challenges in achieving high frequency-sweep linearity and large excursion, which are critical for accurate distance and velocity measurements. Here, we propose a self-injection locked laser with frequency-shifted feedback to generate ultra-linear and wideband FMCW light. A record-low relative frequency nonlinearity of 6.4×10-7 is achieved when the frequency excursion is 100 GHz and the repetition frequency is 1 kHz. In the LiDAR test, a range resolution of 1.6 mm and a velocity accuracy of 3 mm/s at 300 m distance are demonstrated, and those of 8.1 mm and 6 mm/s at 1 km distance are also obtained. The reported FMCW light source provides not only enhanced performance in coherent LiDAR, but also utilization potential in various high-precision measurement scenarios.
Photonics Research
- Publication Date: Dec. 16, 2024
- Vol. 13, Issue 1, 31 (2025)
Dynamic counterpropagating all-normal dispersion (DCANDi) fiber laser
Neeraj Prakash, Jonathan Musgrave, Bowen Li, and Shu-Wei Huang
The fiber single-cavity dual-comb laser (SCDCL) is an emerging light-source architecture that opens up the possibility for low-complexity dual-comb pump-probe measurements. However, the fundamental trade-off between measurement speed and time resolution remains a hurdle for the widespread use of fiber SCDCLs in dual-comb pump-probe measurements. In this paper, we break this fundamental trade-off by devising an all-optical dynamic repetition rate difference (Δfrep) modulation technique. We demonstrate the dynamic Δfrep modulation in a modified version of the recently developed counterpropagating all-normal dispersion (CANDi) fiber laser. We verify that our all-optical dynamic Δfrep modulation technique does not introduce excessive relative timing jitter. In addition, the dynamic modulation mechanism is studied and validated both theoretically and experimentally. As a proof-of-principle experiment, we apply this so-called dynamic CANDi (DCANDi) fiber laser to measure the relaxation time of a semiconductor saturable absorber mirror, achieving a measurement speed and duty cycle enhancement factor of 143. DCANDi fiber laser is a promising light source for low-complexity, high-speed, high-sensitivity ultrafast dual-comb pump-probe measurements. The fiber single-cavity dual-comb laser (SCDCL) is an emerging light-source architecture that opens up the possibility for low-complexity dual-comb pump-probe measurements. However, the fundamental trade-off between measurement speed and time resolution remains a hurdle for the widespread use of fiber SCDCLs in dual-comb pump-probe measurements. In this paper, we break this fundamental trade-off by devising an all-optical dynamic repetition rate difference (Δfrep) modulation technique. We demonstrate the dynamic Δfrep modulation in a modified version of the recently developed counterpropagating all-normal dispersion (CANDi) fiber laser. We verify that our all-optical dynamic Δfrep modulation technique does not introduce excessive relative timing jitter. In addition, the dynamic modulation mechanism is studied and validated both theoretically and experimentally. As a proof-of-principle experiment, we apply this so-called dynamic CANDi (DCANDi) fiber laser to measure the relaxation time of a semiconductor saturable absorber mirror, achieving a measurement speed and duty cycle enhancement factor of 143. DCANDi fiber laser is a promising light source for low-complexity, high-speed, high-sensitivity ultrafast dual-comb pump-probe measurements.
Photonics Research
- Publication Date: Aug. 30, 2024
- Vol. 12, Issue 9, 2033 (2024)
Quantum dot fourth-harmonic colliding pulse mode-locked laser for high-power optical comb generation
Jing-Zhi Huang, Bo Yang, Jia-Jian Chen, Jia-Le Qin, Xinlun Cai, Jie Yan, Xi Xiao, Zi-Hao Wang, Ting Wang, and Jian-Jun Zhang
Quantum-dot mode-locked lasers have advantages such as high temperature stability, large optical bandwidth, and low power consumption, which make them ideal optical comb sources, especially for wavelength-division multiplexing (WDM) telecommunications, and optical I/O applications. In this work, we demonstrate an O-band quantum dot colliding pulse mode-locked laser (QD-CPML) to generate optical frequency combs with 200 GHz spacing with maximum channels of 12 within 3 dB optical bandwidth. To achieve the high output power of individual comb lines, four channel conditions are implemented at central wavelength of 1310 nm for WDM transmission experiments. Each channel exhibits more than 10 dBm output power with 200 Gb/s PAM-4 and 270 Gb/s PAM-8 modulation capability via thin-film LiNbO3 Mach–Zehnder interferometer modulator without the requirement of any optical amplifications. This high-order QD-CPML is an ideal comb source for power-efficient optical interconnects and large bandwidth optical data transmission. Quantum-dot mode-locked lasers have advantages such as high temperature stability, large optical bandwidth, and low power consumption, which make them ideal optical comb sources, especially for wavelength-division multiplexing (WDM) telecommunications, and optical I/O applications. In this work, we demonstrate an O-band quantum dot colliding pulse mode-locked laser (QD-CPML) to generate optical frequency combs with 200 GHz spacing with maximum channels of 12 within 3 dB optical bandwidth. To achieve the high output power of individual comb lines, four channel conditions are implemented at central wavelength of 1310 nm for WDM transmission experiments. Each channel exhibits more than 10 dBm output power with 200 Gb/s PAM-4 and 270 Gb/s PAM-8 modulation capability via thin-film LiNbO3 Mach–Zehnder interferometer modulator without the requirement of any optical amplifications. This high-order QD-CPML is an ideal comb source for power-efficient optical interconnects and large bandwidth optical data transmission.
Photonics Research
- Publication Date: Aug. 29, 2024
- Vol. 12, Issue 9, 1991 (2024)
Dual-frequency optical-microwave atomic clocks based on cesium atoms
Tiantian Shi, Qiang Wei, Xiaomin Qin, Zhenfeng Liu, Kunkun Chen, Shiying Cao, Hangbo Shi, Zijie Liu, and Jingbiao Chen
133Cs, the only stable cesium (Cs) isotope, is one of the most investigated elements in atomic spectroscopy and was used to realize the atomic clock in 1955. Among all atomic clocks, the cesium atomic clock has a special place, since the current unit of time is based on a microwave transition in the Cs atom. In addition, the long lifetime of the 6P3/2 state and simple preparation technique of Cs vapor cells have great relevance to quantum and atom optics experiments, which suggests the use of the 6S-6P D2 transition as an optical frequency standard. In this work, using one laser as the local oscillator and Cs atoms as the quantum reference, we realize two atomic clocks at the optical and microwave frequencies. Both clocks can be freely switched or simultaneously output. The optical clock, based on the vapor cell, continuously operated with a frequency stability of 3.9×10-13 at 1 s, decreasing to 2.2×10-13 at 32 s, which was frequency-stabilized by modulation transfer spectroscopy and estimated by an optical comb. Then, applying this stabilized laser to an optically pumped Cs beam atomic clock to reduce the laser frequency noise, we obtained a microwave clock with a frequency stability of 1.8×10-12/τ, reaching 6×10-15 at 105 s. This study demonstrates an attractive feature for the commercialization and deployment of optical and microwave clocks, and will guide the further development of integrated atomic clocks with better stability. Therefore, this study holds significant practical implications for future applications in satellite navigation, communication, and timing. 133Cs, the only stable cesium (Cs) isotope, is one of the most investigated elements in atomic spectroscopy and was used to realize the atomic clock in 1955. Among all atomic clocks, the cesium atomic clock has a special place, since the current unit of time is based on a microwave transition in the Cs atom. In addition, the long lifetime of the 6P3/2 state and simple preparation technique of Cs vapor cells have great relevance to quantum and atom optics experiments, which suggests the use of the 6S-6P D2 transition as an optical frequency standard. In this work, using one laser as the local oscillator and Cs atoms as the quantum reference, we realize two atomic clocks at the optical and microwave frequencies. Both clocks can be freely switched or simultaneously output. The optical clock, based on the vapor cell, continuously operated with a frequency stability of 3.9×10-13 at 1 s, decreasing to 2.2×10-13 at 32 s, which was frequency-stabilized by modulation transfer spectroscopy and estimated by an optical comb. Then, applying this stabilized laser to an optically pumped Cs beam atomic clock to reduce the laser frequency noise, we obtained a microwave clock with a frequency stability of 1.8×10-12/τ, reaching 6×10-15 at 105 s. This study demonstrates an attractive feature for the commercialization and deployment of optical and microwave clocks, and will guide the further development of integrated atomic clocks with better stability. Therefore, this study holds significant practical implications for future applications in satellite navigation, communication, and timing.
Photonics Research
- Publication Date: Aug. 29, 2024
- Vol. 12, Issue 9, 1972 (2024)
Ultrasensitive detection of remote acoustic vibrations at 300 m distance by optical feedback enhancement|Editors' Pick
Mingwang Tian, Xin Xu, Sihong Chen, Zhipeng Feng, and Yidong Tan
Sensitive detection of remote vibrations at nanometer scale owns promising potential applications such as geological exploration, architecture, and public security. Nevertheless, how to detect remote vibration information with high sensitivity and anti-disturbance has become a major challenge. Reported current non-contact measurement methods are difficult to simultaneously possess characteristics of high light intensity sensitivity, long working distance, high vibration response sensitivity, and anti-disturbance of ambient light. Here, we propose a polarization-modulated laser frequency-shifted feedback interferometry method with the above characteristics, to obtain remote vibration information. The method can directly measure non-cooperative targets without the need for any cooperative markers. In each interference cycle, the energy as low as 2.3 photons can be effectively responded to, and the vibration amplitude sensitivity at 300 m can reach 0.72 nm/Hz1/2 at 1 kHz. This approach provides a strategy for the ultrasensitive detection of remote vibration that is immune to electromagnetic interference. Sensitive detection of remote vibrations at nanometer scale owns promising potential applications such as geological exploration, architecture, and public security. Nevertheless, how to detect remote vibration information with high sensitivity and anti-disturbance has become a major challenge. Reported current non-contact measurement methods are difficult to simultaneously possess characteristics of high light intensity sensitivity, long working distance, high vibration response sensitivity, and anti-disturbance of ambient light. Here, we propose a polarization-modulated laser frequency-shifted feedback interferometry method with the above characteristics, to obtain remote vibration information. The method can directly measure non-cooperative targets without the need for any cooperative markers. In each interference cycle, the energy as low as 2.3 photons can be effectively responded to, and the vibration amplitude sensitivity at 300 m can reach 0.72 nm/Hz1/2 at 1 kHz. This approach provides a strategy for the ultrasensitive detection of remote vibration that is immune to electromagnetic interference.
Photonics Research
- Publication Date: Aug. 29, 2024
- Vol. 12, Issue 9, 1962 (2024)
Generating broadband cylindrical vector modes based on polarization-dependent acoustically induced fiber gratings using the dispersion turning point
Meiting Xie, Jiangtao Xu, Jiajun Wang, Huihui Zhao, Yeshuai Liu, Jianxiang Wen, Fufei Pang, Jianfeng Sun, and Xianglong Zeng
Cylindrical vector beams (CVBs) with special polarization distribution have been extensively investigated due to the unique ways of interacting with matter. Although several configurations have been developed to generate CVBs, such as Q-plates and subwavelength gratings, the bandwidth of a single CVB is inherently narrow due to the phase geometry, which would limit its application for femtosecond lasers. Here, a broadband CVB mode converter based on an acoustically induced fiber grating (AIFG) and a tuning method of dispersion turning point (DTP) is demonstrated both theoretically and experimentally with the 3-dB bandwidth of 125 nm, which is more than 10 times that of conventional AIFGs. Not only can the DTP wavelength be tuned from the original 1500 nm to 1650 nm by thinning the fiber, but also the stable generation of a single broadband HE21odd/even mode can be controllably implemented by adjusting the polarization state of the incident light, owing to the larger beat length difference between HE21 and other CV modes. Additionally, the femtosecond CVBs and orbital angular momentum (OAM) modes are successfully generated and amplified by combining the broadband AIFG with a figure-9 mode-locked fiber laser. Meanwhile, it is verified by simulation that the choice of broadband CV mode and the tunability of DTP wavelength can be realized by designing ring-core fibers with different structures, which can furthermore improve the flexibility of generating high purity CVBs. This study provides a highly controllable technique for the generation of broadband CVBs and OAMs paving the way for high-capacity CVBs communication. Cylindrical vector beams (CVBs) with special polarization distribution have been extensively investigated due to the unique ways of interacting with matter. Although several configurations have been developed to generate CVBs, such as Q-plates and subwavelength gratings, the bandwidth of a single CVB is inherently narrow due to the phase geometry, which would limit its application for femtosecond lasers. Here, a broadband CVB mode converter based on an acoustically induced fiber grating (AIFG) and a tuning method of dispersion turning point (DTP) is demonstrated both theoretically and experimentally with the 3-dB bandwidth of 125 nm, which is more than 10 times that of conventional AIFGs. Not only can the DTP wavelength be tuned from the original 1500 nm to 1650 nm by thinning the fiber, but also the stable generation of a single broadband HE21odd/even mode can be controllably implemented by adjusting the polarization state of the incident light, owing to the larger beat length difference between HE21 and other CV modes. Additionally, the femtosecond CVBs and orbital angular momentum (OAM) modes are successfully generated and amplified by combining the broadband AIFG with a figure-9 mode-locked fiber laser. Meanwhile, it is verified by simulation that the choice of broadband CV mode and the tunability of DTP wavelength can be realized by designing ring-core fibers with different structures, which can furthermore improve the flexibility of generating high purity CVBs. This study provides a highly controllable technique for the generation of broadband CVBs and OAMs paving the way for high-capacity CVBs communication.
Photonics Research
- Publication Date: Aug. 26, 2024
- Vol. 12, Issue 9, 1907 (2024)
Twenty-milliwatt, high-power, high-efficiency, single-mode, multi-junction vertical-cavity surface-emitting lasers using surface microstructures
Yao Xiao, Pei Miao, Jun Wang, Heng Liu, Yudan Gou, Zhicheng Zhang, Bangguo Wang, Wuling Liu, Qijie Wang, Guoliang Deng, and Shouhuan Zhou
High-power, high-efficiency single-mode vertical-cavity surface-emitting lasers (VCSELs) are crucial in the realm of green photonics for high-speed optical communication. However, in recent years, the power and efficiency of single-mode VCSELs have remained relatively low and have been progressing slowly. This study combines theoretical models with experiments to show that multi-junction cascaded 940 nm VCSELs based on surface microstructures can achieve high power, high efficiency, and low divergence in single-mode laser output. Simulations show multi-junction VCSELs with surface microstructures can boost mode modulation capabilities, power, and efficiency, potentially allowing high-power single-mode VCSELs to surpass 60% efficiency. Using this technique, the 6 μm oxide aperture VCSELs with surface relief of different diameters were fabricated. The single-mode VCSELs with the output power of 20.2 mW, side-mode suppression ratios greater than 35 dB, 42% electro-optical efficiency, and a 9.8° divergence angle (at 1/e2) under continuous-wave operation were demonstrated. Near-field images verified its fundamental mode operation. To the best of the authors’ knowledge, this is the highest single-mode power recorded for a single-unit VCSEL to date, almost twice the currently known record, while still maintaining a very high electro-optical conversion efficiency. This research will provide valuable references for the further development and application of high-power, high-efficiency single-mode semiconductor lasers. High-power, high-efficiency single-mode vertical-cavity surface-emitting lasers (VCSELs) are crucial in the realm of green photonics for high-speed optical communication. However, in recent years, the power and efficiency of single-mode VCSELs have remained relatively low and have been progressing slowly. This study combines theoretical models with experiments to show that multi-junction cascaded 940 nm VCSELs based on surface microstructures can achieve high power, high efficiency, and low divergence in single-mode laser output. Simulations show multi-junction VCSELs with surface microstructures can boost mode modulation capabilities, power, and efficiency, potentially allowing high-power single-mode VCSELs to surpass 60% efficiency. Using this technique, the 6 μm oxide aperture VCSELs with surface relief of different diameters were fabricated. The single-mode VCSELs with the output power of 20.2 mW, side-mode suppression ratios greater than 35 dB, 42% electro-optical efficiency, and a 9.8° divergence angle (at 1/e2) under continuous-wave operation were demonstrated. Near-field images verified its fundamental mode operation. To the best of the authors’ knowledge, this is the highest single-mode power recorded for a single-unit VCSEL to date, almost twice the currently known record, while still maintaining a very high electro-optical conversion efficiency. This research will provide valuable references for the further development and application of high-power, high-efficiency single-mode semiconductor lasers.
Photonics Research
- Publication Date: Aug. 26, 2024
- Vol. 12, Issue 9, 1899 (2024)
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