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A low-noise Brillouin random fiber laser (BRFL) based on dynamic fiber grating (DFG)-assisted self-injection locking (SIL) as a laser carrier for coherent communication is proposed and experimentally demonstrated. The utilization of the DFG-based SIL basically guarantees an innovative purification of ultra-narrow-linewidth laser radiation after the removal of residual random modes from the gain competition, enabling unprecedented long-term frequency-stabilized coherent lasing resonance over a record of 30 s. Consequently, the relative intensity noise of the generated Stokes random laser is significantly suppressed by ∼20 dB, and the frequency/phase noise imposed by random mode hopping is additionally mitigated. Meanwhile, stimulated Brillouin scattering and randomly distributed Rayleigh scattering along the kilometer-long single-mode fiber further suppress laser frequency/phase noise, benefiting the ultra-narrow laser linewidth of 450 Hz. As a proof-of-concept, an 8-Gbaud (32 Gb/s) 16-quadrature amplitude modulation transmission based on the proposed self-injection locked low-noise BRFL as the laser carrier is demonstrated, achieving a low bit error rate of 3.02 × 10 − 5 . The impact of the laser noise on coherent communication is systematically investigated, highlighting the potential in high-capacity coherent communication. [ABSTRACT FROM AUTHOR]

Soliton microcombs, offering large mode spacing and broad bandwidth, have enabled a variety of advanced applications, particularly for telecommunications, photonic data center, and optical computation. Yet, the absolute power of microcombs remains insufficient, such that optical power amplification is always required. Here, we demonstrate a combined technique to access power-sufficient optical microcombs, with a photonic-integrated soliton microcomb and home-developed erbium-doped gain fiber. The soliton microcomb is generated in an integrated Si 3 N 4 microresonator chip, which serves as a full-wave probing signal for power amplification. After the amplification, more than 40 comb modes, with 115-GHz spacing, reach the onset power level of >−10 dBm, which is readily available for parallel telecommunications , among other applications. [ABSTRACT FROM AUTHOR]

Er-doped optical fiber (EDF) with ultra-broad gain bandwidth is urgently needed given the rapid advancement of optical communication. However, the weak crystal field of the host silica glass severely restricts the bandwidth of traditional EDF at 1.5 μm. In this study, we theoretically explored the introduction of PbS nanomaterials in the silica network assisted with the non-bridging oxygen. This can significantly increase the crystal field strength of Er3+ ions in the local structure, leading to their energy level splitting and expanding the fluorescence bandwidth. Additionally, the PbS/Er co-doped optical fiber (PEDF) with improved fluorescence and gain characteristics was fabricated using modified chemical vapor deposition combined with the atomic layer deposition technique. The presence of PbS nanomaterials in the fiber core region, which had an average size of 4 nm, causes the 4I13/2 energy level of Er3+ ions to divide, increasing the fluorescence bandwidth from 32 to 39 nm. Notably, the gain bandwidth of PEDF greater than 20 dB increased by approximately 12 nm compared to that of EDF. The obtained PEDF would play an important role in the optical fiber amplifier and laser applications. [ABSTRACT FROM AUTHOR]

Two kinds of Yb-doped fibers were fabricated, namely, Yb: YAG crystal-derived silica fibers (YCDSFs) with a gain coefficient of 6.0 dB/cm, and Bi/Er/Yb co-doped silica fibers having a Yb concentration of 0.13 $ \times $ 1026 ions/m3. Based on these fibers, a ring-cavity single-frequency fiber laser (SFFL) has been constructed, in which the YCDSF was used as a gain medium and the Bi/Er/Yb co-doped fiber acted as a saturable absorber. It has been demonstrated that the SFFL had an over 100 mW output at 1030 nm, a slope-efficiency of up to 18.3%, and an optical signal-to-noise ratio of over 63 dB. The fluctuation of the output power of the laser was less than 0.65% of 103.5 mW within 10 hrs and no mode-hopping was observed for 5 hrs. The SFFL had a linewidth <7.5 kHz at the maximum output power, and the measured relative intensity noise was lower than −142 dB/Hz at the frequency above 1.0 MHz. The results indicate that the ring-cavity SFFL built could be used as a laser source for applications in high-power fiber laser and high-precision optical fiber sensing and detection. [ABSTRACT FROM AUTHOR]

We have experimentally demonstrated the flat supercontinuum (SC) generation using a 10-m-long ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fluoride fiber pumped by an erbium-doped mode-locked fiber laser incorporating carbon-nanotube-based saturable absorbers. In order to improve the spectral flatness of SC, the standardized single-mode fiber with different lengths is connected to the output of the mode-locked fiber laser before the pulse amplification. The generated SC with ZBLAN fiber exhibits the best spectral flatness with fluctuation less than 1.29dB over the wavelength of 1571.8nm–1803.1nm, showing potential applications in optical sensing. [ABSTRACT FROM AUTHOR]

We have reported high-energy pulse generation from a Q-switched Er-doped fiber laser based on black phosphorus (BP) with a drop-casting method. Poly dimethyl diallyl ammonium (PDDA) is employed to protect BP. A passive Q-switching operation is achieved by using the BP/polyvinyl alcohol (PVA) film as the saturable absorbers (SAs). When the pump power increases from 130.4 mW to 378 mW, the repetition rate increases from 13.33 kHz to 26.6 kHz, and the pulse duration decreases from 10.67 μs to 7.11 μs. The maximum pulse energy is 468.03 nJ, to the best of our knowledge, which is the highest pulse energy produced from Q-switched fiber laser based on BP-SA at 1.5 μm. The obtained high-energy pulse demonstrates that BP/PVA film fabricated by such a drop-casting method can provide an ideal SA for high pulse energy generation from fiber lasers, and it has a potential application of remote sensing. [ABSTRACT FROM AUTHOR]

We demonstrate the fabrication of helical long-period gratings (HLPGs) with the periodic helical index modulation by twisting the double-clad fiber (DCF) while the fiber was exposed by CO2 laser. Torsion, bending, surrounding refractive index, temperature and axial strain characteristics of the fabricated DCF-HLPG were investigated experimentally. The DCF-HLPG was found to have a high torsion sensitivity of −0.384 nm/(rad/m) and bending sensitivity of 18.112 nm/m−1 due to the asymmetric helical index modulation across the fiber section induced by the CO2 laser heating. [ABSTRACT FROM AUTHOR]

In active silica optical fibers, improving the solubility and uniformity of non-concentration-quenching luminescence centers is a key strategy to achieve high gain fiber amplifiers. Herein, we report a novel Er-doped silica optical fiber (EDF) modified by PbS semiconductor incorporation for the first time. Owing to the bridge role of PbS, Er 2 O 3 nanofilms deposited on the substrate via atomic layer deposition (ALD) have porous and loosely layered network structures with an increasing number of ALD-PbS layers. Subsequently, during the high-temperature fiber preparation process, this loose porous structure aids the dissolution and provides an optimal local environment of Er3+ ions in the silica matrix. As a result, the maximum phonon energy of the silica network for PbS/Er co-doped silica optical fiber (PEDF) is reduced, resulting in an increase of the Er3+ ion fluorescence lifetime, approximately 11.455 ms. Furthermore, we achieved 34 dB maximum gain of PEDF sample with the lowest noise figure of 3.9 dB at 1.5 μm. The gain bandwidth over 20 dB of PEDF is approximately 46 nm, which is nearly 44% higher than that of EDF. These results indicate that the PEDF prepared by structural manipulation has great potentials in optical fiber amplifier and laser applications. • Porous PbS/Er co-doped nanofilms were prepared and characterized. • PbS and Er co-doped silica fibers (PEDF) were fabricated for the first time. • Er3+ ions in PEDF show more uniform distribution and higher fluorescence efficiency. • PEDF has the high gain of 34 dB and low NF of 3.9 dB in the amplification system. • Gain bandwidth of PEDF are increased by 44% compared to the non-PbS doped EDF. [ABSTRACT FROM AUTHOR]

We experimentally demonstrated a high-order optical vortex pulsed laser based on a mode selective all-fiber fused coupler composed of a single-mode fiber (SMF) and a few-mode fiber (FMF). The fused SMF-FMF coupler inserted in the cavity acts as a mode converter from LP01 mode to LP11 (LP 21) mode with a broadband width. Linearly polarized OAM modes can be obtained by combining different vector modes HE2,m^{even} (HE2,m^{odd} ) and TE0,m (TM 0,m) when l = 1 or combining HEl+1,m^{even} (HE l+1,m^{odd}) and EH l-1,m^{odd} (EH l-1,m^{even}) when l > 1 with a \pi /2 phase shift. To the best of our knowledge, this is the first report on the generation of high-order pulse vortex beams in a mode-locked fiber laser. The measured time duration of OVB pulses is 273 fs, 140 fs of OAM\pm 1 and OAM \pm 2. [ABSTRACT FROM PUBLISHER]

We experimentally obtain femtosecond cylindrical vector beams based on a mode-locked fiber laser (MLFL) by using a fused few-mode coupler. Pulses of 300 fs duration with radially and azimuthally polarized modes are directly delivered at the central wavelength of 1566 nm. The fused few-mode fiber coupler inserted inside the cavity acts as a mode converter from LP01 mode to LP11 mode with a wide bandwidth over 100 nm. The proof-of-concept generation of femtosecond cylindrical vector beams is efficient and useful in MLFLs. [ABSTRACT FROM PUBLISHER]

We propose a simple and compact method for implementing an in-fiber Mach–Zehnder interferometer, which is constructed with two optical paths, propagating through the core and the ring-shaped silica cladding modes in the double-cladding fibers. Strong cladding-mode resonance across the thin inner cladding is used to excite the cladding modes. The measured spectra fringe presents high-contrast interference from cascading a pair of well-overlapped resonant spectra dips. In combination with the nonlinear polarization rotation (NPR) technique, switchable and tunable multi-channel laser outputs are experimentally demonstrated with a fluctuation of less than 0.1 dB. [ABSTRACT FROM AUTHOR]

We fabricated a novel Pb/Bi co-doped silica optical fiber using an atomic layer deposition technique in conjunction with a modified chemical vapour deposition process. The fabricated fiber exhibits distinct absorption peaks at 690, 800, 1000 and 1377 nm. An ultra-broad luminescence band with a 10 dB bandwidth of 600 nm from 1050 nm to 1650 nm was achieved using a dual pumps system. The lifetime of the co-doped fiber at 1150 nm is approximately 740 μs. Additionally, a Pb/Bi co-doped fiber with a length of only 0.2 m, pumped at 980 nm exhibits an optical gain ranging from 1010 to 1190 nm with a maximum peak gain of 12 dB. A theoretical model considering the interaction between Pb and Bi ions is proposed to interpret the observed spectral characteristics. There may be a coupling effect and/or energy transfer between Pb and Bi ions during a deleterious non-radiative quenching process. The Pb/Bi co-doped fiber offers a number of advantages compared to a conventional Bi-doped fiber in terms of broadband luminesce, fluorescence lifetime, and gain. Additionally, it can act as a super fluorescence fiber sources for optical amplifiers and novel fiber lasers in the medical and communication fields. • A novel Pb/Bi co-doped silica optical fiber is fabricated using an atomic layer deposition doping technique. • The 10 dB luminescence bandwidth of Pb/Bi co-doped silica optical fiber is up to 600 nm. • A Pb/Bi co-doped fiber with 0.2 m length shows the optical gain is up to 12 dB range from 1010 to 1190 nm. • A theoretical model is proposed to elucidate the effect of the introduction of Pb ions on Bi-doped fiber. [ABSTRACT FROM AUTHOR]

The cerium (Ce)-doped optical fiber materials show great applications in smart lighting, fiber laser, and high-energy ray and particle detection. A major challenge is the efficient prevention of Ce3+ oxidized to Ce4+ ions. Here we report the CO 2 -laser-heated drawing method for fabricating Ce:YAG derived scintillating optical fiber with a concentration of Ce ions (0.21 wt%), and the effective atomic number is 25.4. The estimated ratio of Ce4+/ΣCe is 37% in the raw YAG ceramics, which can be effectively reduced to 3% in the fiber core because of the negative oxygen atmosphere during the fiber drawing process and the formation of non-bridging oxygen. The result is confirmed by the optical absorption spectrum, X-ray absorption fine structure spectra (XAFS), and Raman spectra. These induce a strong emission peak at 401 nm under the X-ray excitation. Moreover, the normalized integral scintillation efficiency of the Ce:YAG derived fiber is up to ~43% of that of Bi 4 Ge 3 O 12 (BGO) scintillating crystal. The Ce:YAG derived optical fiber is believed to be a promising candidate for scintillators in remote fiber-optic radiation detection applications. • Ce:YAG derived fiber was fabricated using the CO 2 -laser-heated method. • The ratio of Ce3+/Ce4+ ions in the fiber was evaluated with the XAFS. • The Ce3+ ions play an important role in the scintillation process of Ce:YAG derived fiber. • High scintillation efficiency of Ce:YAG derived fiber with the excitation of X-ray. • Significant linear RL response of Ce:YAG derived fiber for the X-rays detection. [ABSTRACT FROM AUTHOR]