Search Results (23)

Laser-induced exit surface damage of fused silica is a key bottleneck for its application in high-power laser devices. As low-temporal coherence light (LTCL) has garnered increasing attention for high-power laser-driven inertial confinement fusion, understanding LTCL-induced exit surface damage of fused silica becomes crucial for improving the output power capability of LTCL devices. In this study, we characterized damage on the exit surface of fused silica under LTCL irradiation and investigated the physical mechanism of temporal coherence affecting the laser-induced damage threshold (LIDT). The relationship between defect information and temporal coherence was explored using a defect analysis model, and the defect damage process and response to each incident lasers were captured using time-resolved methods and artificially fabricated defects. We elucidate the physical mechanism behind the lower LIDT under LTCL irradiation compared to single longitudinal mode (SLM) pulse lasers. This study not only provides the boundary condition for safe fused silica operation in high-power LTCL devices but also offers deeper insight into the physical properties of LTCL. Full article

An all-optical single-longitudinal-mode (SLM) forward Brillouin microwave oscillator (FB-MO) with an unbalanced Fiber Mach–Zehnder interferometer (UF-MZI) for microwave photonics (MWP) generation is proposed and experimentally investigated. UF-MZI consists of an optical coupler (OC), a polarization controller (PC), and two asymmetric length arms with 5 km and 500 m single-mode fibers (SMFs), which implements two unbalanced length feedback rings that are connected to one another. One long-length ring with a forward Brillouin gain cooperates with the other short-length ring to maintain a spectral Vernier effect and improve the effective free spectral range (FSR). By contrast with traditional optoelectronic oscillators (OEOs), this design does not require any photoelectric conversion devices and additional modulation, avoids external electromagnetic interference, and side-mode suppression and linewidth are favorable. Experimental results reveal that the 3-dB linewidth of the all-optical SLM FB-MO with UF-MZI is about 140 Hz. The acoustic-mode and side-mode suppression ratios are 26 dB and 31 dB. Within 60 min of the stability experiment, the power and frequency stability fluctuation were ±1 dB and ±100 Hz. Thanks to its long main ring cavity length, our all-optical SLM FB-MO with UF-MZI maintains good phase-noise performance. The measurement shows that a phase noise as low as −120 dBc/Hz at an offset frequency of 100 kHz is achieved. This SLM MWP generation technology holds great potential for applications in radar monitoring and wireless communication systems. Full article

A Hz level narrow linewidth all-optical microwave oscillator based on the torsional radial acoustic modes (TR_2,m) of a single-mode fiber (SMF) is proposed and validated. The all-optical microwave oscillator consists of a 20 km SMF main ring cavity and a 5 km SMF sub ring cavity. The main ring cavity provides forward stimulated Brillouin scattering gain and utilizes a nonlinear polarization rotation effect to achieve TR_2,7 mode locking. By combining the sub ring cavity with the main ring cavity and utilizing the Vernier effect, the TR_2,7 mode microwave photonic single longitudinal mode (SLM) output can be ensured. Meanwhile, the 6.281 Hz narrow linewidth of the TR_2,7 mode is achieved by reducing the intrinsic linewidth of the passive resonant cavity. The acoustic mode suppression ratio and side mode suppression ratio of the TR_2,7 mode were 43 dB and 54 dB, respectively. The power and frequency fluctuations of within 40 min were approximately ±0.49 dB and ±0.187 kHz, indicating good stability. At a frequency offset of 10 kHz, the TR_2,7 mode had a low phase noise value of −110 dBc/Hz. This solution can be used in various fields, such as high-precision radar detection, long-distance optical communication, and high-performance fiber optic sensing. Full article

A low-cost, wavelength-tunable single-longitudinal-mode (SLM) thulium–holmium co-doped fiber laser (THDFL) in a 2 μm band with a simple structure is described in the present paper. To obtain a stable SLM and narrow laser linewidth, a five-coupler-based three-ring (FCTR) filter is utilized in the ring cavity of the fiber laser. Tunable SLM wavelength output from THDFLs with kHz linewidths can be achieved by designing the FCTR filter with an effective free-spectral range and a 3 dB bandwidth at the main resonant peak. The measurement results show that the laser is in the SLM lasing state, with a highly stabilized optical spectrum, a linewidth of approximately 9.45 kHz, an optical signal-to-noise ratio as high as 73.6 dB, and a relative intensity noise of less than −142.66 dB/Hz. Furthermore, the wavelength can be tuned in the range of 2.6 nm. The proposed fiber laser has a wide range of applications, including coherence optical communication, optical fiber sensing, and dense wavelength-division-multiplexing. Full article

A thulium-doped fiber laser (TDFL) with a dual-active cavity and a directly linked three-coupler triple-ring filter is designed and demonstrated. Its operational principle is analyzed, and a corresponding experimental setup is built. Eleven single-wavelength laser outputs with a single-longitudinal-mode (SLM) output near 2 μm are obtained. The laser output covers a wavelength range from 1933.95 nm to 1971.76 nm, with a continuous switchable output range of 37.81 nm and a minimum center wavelength interval of 0.22 nm. The optical signal-to-noise ratio (OSNR) of the output laser within the tuning range is >48.53 dB, and its maximum OSNR is 70.24 dB. The minimum wavelength fluctuation is 0.03 nm, and the power fluctuation is between 0.15 and 2.61 dB. A single wavelength with a center wavelength of 1933.95 nm is monitored for 75 min, and the radio-frequency spectrum is scanned 27 times within the frequency range of 0 to 400 MHz. The results demonstrate that the TDFL can operate continuously and stably in an SLM state. The linewidth and linewidth fluctuation of the TDFL are measured, and the minimum linewidth, corresponding to a measurement time of 0.001 s, is 65.14 kHz. The experimental results show that the proposed TDFL has a high OSNR and excellent wavelength-switching ability, and its SLM operation is very stable. Full article

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. Full article

This work demonstrates a high-quality erbium-doped fiber (EDF) ring laser in the L-band gain range by combining the Rayleigh backscattering (RB) feedback signal and unpumped EDF induced saturable absorber (SA) filter. The optical filter effect induced by the RB feedback injection and EDF SA could generate single-longitudinal-mode (SLM) behavior and shrink the linewidth to sub-kHz. The output linewidth, power, and optical-signal-to-noise ratio (OSNR) of the fiber ring laser were also shown within the 42 nm wavelength bandwidth of 1565.0 to 1607.0 nm. Also, the instabilities of output power and central wavelength of each lasing lightwave were analyzed with a measurement time of 45 min. Full article

A new vibration-based mechanism of optical frequency/wavelength sweeping in fiber lasers induced by optical path length modulation of a laser cavity section is proposed. The mechanism is implemented for an erbium-doped fiber ring laser with a saturable absorber. Without the vibrations, the laser generates a single longitudinal mode (SLM) radiation. We show experimentally for the first time that mechanical vibrations of the laser cavity section can lead to mode dynamics in both frequency and time domains. The possibility of obtaining various mode dynamics, such as vibration-induced sweeping in a wavelength range of up to 2.2 nm or SLM generation with periodic mode hopping between two fixed longitudinal modes depending on the pump wavelength, is experimentally shown. In this vibration-based approach, the interval between changes in the laser cavity modes has good stability, because it directly relates to the vibration period. Full article

In this demonstration, we present two erbium-doped fiber (EDF) lasers, with series and parallel three sub-ring configurations, respectively, to achieve tunable channel output and stable single longitudinal mode (SLM) operation in the L-band range. Here, the fiber ring cavity contains the L-band EDF as a gain medium. Based on the measured results of the two quad-ring structures of the EDF lasers, tunable output bandwidth for the two lasers can be obtained from 1558.0 to 1618.0 nm simultaneously. All the 3 dB linewidths measured for both fiber lasers are 312.5 Hz over the effective wavelength output range. Furthermore, the related optical signal-to-noise ratio (OSNR), output power, output stabilities of the central wavelength and power, and equal output power range of the two proposed EDF lasers are also examined and discussed. Full article

This paper presents experimental evidence regarding a novel switchable dual-wavelength thulium-doped fiber laser (TDFL). Wavelength switching is achieved by combining a polarization-maintaining fiber Bragg grating (PM-FBG) with a polarization controller (PC). The three-coupler double-ring compound cavity (TC-DRC) structure, acting as a mode-selection filter, is designed to select a single longitudinal mode (SLM) from the dense longitudinal modes. This paper introduces the design and fabrication method of the TC-DRC filter and analyzes, in detail, the mechanism for SLM selection. The experimental results demonstrate that the designed filter exhibits excellent performance. By adjusting the PC, the TDFL achieves stable SLM operation at the wavelengths of 1940.54 nm and 1941.06 nm, respectively. The optical signal-to-noise ratio (OSNR) is superior to 65 dB. When the TDFL is tested at room temperature, there is no significant wavelength drift, and power fluctuations are less than 1.5 dB. The operation of the SLM is verified through the self-heterodyne method, and the laser maintains stable SLM states for both wavelengths after continuous operation for an hour. Furthermore, based on the phase noise demodulation method, the linewidths of both wavelengths are measured to be less than 10 kHz at the integration time of 0.001 s. Full article

In this paper, a wavelength-selectable erbium-doped fiber (EDF) laser in L-band bandwidth with a simple structure and low cost is described. To obtain stable single-longitudinal-mode (SLM) and narrow laser linewidth, the 2 m unpumped EDF-based saturable absorber (SA) and 100 m single-mode fiber (SMF)-induced Rayleigh backscattering (RB) injection effect are cascaded in the ring cavity of the fiber laser. The EDF SA and feedback RB injection can cause the auto-tracking ultra-narrow bandwidth filter effect to suppress the multiple longitudinal mode oscillations and narrow the laser linewidth. Thus, the tunable SLM wavelength output of the EDF laser with sub-kHz linewidth can be achieved. In the measurement, two EDF ring lasers can be executed when the placement of EDF-based SA and SMF-induced RB are switched to experiment with different output characteristics. The experimental results show that the wavelength bandwidths of the two lasers are between 1558.0 and 1618.0 nm. Additionally, the optimal optical signal-to-noise ratio (OSNR), wavelength linewidth, output power, and stability of the presented EDF laser configuration are also achieved and discussed. Full article

We create a rate equation theoretical model of a continuous-wave end-pumped Pr³⁺:YLF SLM laser that characterizes the output properties of a single-longitudinal-mode (SLM) green laser. After inserting two Fabry–Perot (F–P) etalons with thicknesses of 0.3 mm and 0.5 mm and angles of 1.42° and 0.69° into the cavity, a single-longitudinal-mode green laser was generated. The maximum output power in single-longitudinal mode was 183 mW. The maximum absorbed pump power was 6.2 W. The corresponding linewidth is about 18 MHz. This work presents a simple method for generating a single-longitudinal-mode laser in the green spectral region, providing a practical approach for various green-laser-related applications. Full article

This article describes a master oscillator and power amplifier (MOPA) system with a single longitudinal mode (SLM) and high-repetition-frequency Pr³⁺:YLF active medium that was end-pumped by two 444 nm laser diodes. The Pr³⁺:YLF MOPA laser system produced a maximum pulse energy of 13.5 μJ with a pulse width of 130.2 ns at a pulse repetition frequency of 20 kHz, translating to a peak power of around 103.7 W. The Pr³⁺:YLF MOPA laser system’s output wavelength was 639.7 nm, and the line-width of its laser spectra was roughly 168 MHz. Additionally, at the highest output level, the laser beam quality did not decrease much due to amplification. Full article

A wavelength-tunable single-longitudinal-mode (SLM) narrow-linewidth thulium/holmium co-doped fiber laser (THDFL) was developed in this study. The lasing wavelength was determined by combining a phase-shifted fiber Bragg grating (PS-FBG) and a uniform FBG (UFBG). SLM oscillation was achieved by incorporating a dual-coupler ring filter with the PS-FBG. At a pump power of 2.0 W, the THDFL exhibited excellent SLM lasing performance with a stable optical spectrum. It operated at an output wavelength of ~2050 nm with an optical signal-to-noise ratio of >81 dB, an output power fluctuation of 0.15 dB, a linewidth of 8.468 kHz, a relative intensity noise of ≤−140.32 dB/Hz@≥5 MHz, a slope efficiency of 2.15%, and a threshold power of 436 mW. The lasing wavelength tunability was validated experimentally by stretching the PS-FBG and UFBG simultaneously. The proposed THDFL had significant potential for application in many fields, including free-space optical communication, LiDAR, and high-precision spectral measurement. Full article

A continuous wave (CW) ultra-narrow linewidth single-longitudinal mode (SLM) ytterbium-doped fiber laser (YDFL) based on narrowband fiber Bragg grating (NB-FBG) and double-ring passive subcavity (DR-PS) was studied. The filtering characteristics of the double-ring passive subcavity are analyzed theoretically, and it is used as a high-precision mode filter to eliminate the dense longitudinal mode and mode hopping of YDFL and ensure that the laser operates in the SLM state. Experimental results show that the laser has a central wavelength of 1030.052 nm at room temperature, an optical signal-to-noise ratio of up to 73 dB, and an ultra-narrow linewidth of 355 Hz. In addition, we measured the short-term and long-term stability of the laser, with wavelength and power fluctuations of less than 0.008 nm and 0.19 dB, respectively, over 120 min. As a result, we obtain SLM YDFL with high stability, ultra-narrow linewidth, and a high optical signal-to-noise ratio. Full article