KEYWORDS: Fiber lasers, L band, Rayleigh scattering, Optical fibers, Laser frequency, Single mode fibers, Random lasers, Laser scattering, Laser damage threshold, Signal to noise ratio
We proposed and experimentally demonstrated a tunable L-band narrow-linewidth Brillouin random fiber laser (BRFL) in a half-open ring cavity with Brillouin gain medium of 10-km single mode fiber (SMF) as well as distributed Rayleigh feedback provided by another 20-km SMF. With a low laser threshold of 6.8mW, the proposed laser can realize cavity-mode-free lasing resonance at a wavelength of 1576.08nm, indicating good single-frequency lasing operation. Compared with the Brillouin pump, the frequency noise (FN) of the proposed laser is significantly suppressed by around 30dB, benefiting from randomly distributed Rayleigh scattering along SMF. An ultra-narrow laser linewidth of 400.8Hz is also obtained with a pump/Stokes laser linewidth compression ratio of 87.5, which coincides with theoretical prediction. When the wavelength of the proposed laser is tuned from 1568.08nm to 1576.08nm, sub-kHz random lasers with cavity mode free lasing resonance achieves high optical signal-to-noise ratio (ONSR) operation. The proposed laser source with good tunability has great potentials for practical applications in future advanced optical communication and sensing.
We reported a narrow-linewidth Brillouin fiber swept laser in a half-open ring cavity based on Brillouin gain medium of a 100-m high nonlinearity fiber (HNLF) as well as distributed Rayleigh random feedback from 1-km single mode fiber (SMF). Thanks to Rayleigh-assistant random lasing resonance, the proposed Stokes laser realizes SLM frequency sweeping radiation as a swept Brillouin pump laser source launched into the random laser cavity. The static linewidth and frequency noise of the Brillouin fiber swept laser is also characterized, which exhibits a linewidth narrowing by over 100 times as well as ~18 dB frequency noise (FN) suppression compared with the pump laser. Results show that the output power and flatness of the Stokes laser were dependent on the sweeping speed of the pump. Demodulated by an unbalanced Mach-Zender interferometer (UMZI), a continuous sweeping range of ~126.33 MHz was obtained during an observation time window of 100 us.
In this work, we fabricated a few mode S-shape waveguide with a length of 20 cm by photolithography, the S-shape waveguide is designed with the minimum bending radius of 8 mm and the maximum bending radius of 13.7 mm. The waveguide core size is 15 μm × 10 μm, and the core pitch is 250 μm. The transmission loss of the waveguide is 0.22 dB/cm at 1310 nm and 0.64 dB/cm at 1550 nm, received by a multimode fiber. While, when the output is received with a single mode fiber, the corresponding values become 0.27 dB/cm at 1310 nm and 0.71 dB/cm at 1550 nm. The crosstalk of the waveguide is lower than -40 dB at 1310 nm.
We have proposed a design of a single side-nickel-core optical fiber (SNCF) and fabricated it using direct thermal drawing for the first time. In our scheme, the metallic-silica heterogenous optical fiber structure was firstly designed and theoretically analyzed by COMSOL, and then thermally drawn from a nickel rod in silica tube preform. The transmission loss of the SNCF at the wavelength of 1550 nm was about 2.28 dB/m. Proven by the microscope observation, the nickel could be well distributed in the side-core of the fiber. It was also proven that the magnetic properties of nickel-core were well preserved after the fiber drawing process. The proposed fiber fabrication method and characterization may be extended to a wide range of other metal-silica heterogenous fibers.
A distributed optical fiber magnetic field sensor based on polarization-sensitive optical frequency domain reflectometer (POFDR) is proposed. The sensor employs a novel distributed magnetic field measurement method that firstly extracts the magnetic field induced nonreciprocal circular birefringence by the combination of the Stokes vectors and the backward Mueller matrices from the measured state of polarization (SOP). Then, the accumulated Faraday rotation angles can be further calculated to characterize the distribution of the magnetic field. It overcomes the drawback of the conventional POFDR scheme that requires at least two different input SOPs for each sensing. Finally, the aforementioned effectiveness has been experimentally verified by using a single-mode fiber as the sensing fiber. The distribution of a static magnetic field in milliTesla has been successfully measured at a spatial resolution of 0.16 m.
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