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We report a novel PbS/Er co-doped silica fiber (PEDF) with improved spectral properties in O-band (1260–1360 nm). The results show that the gain of the PEDF exceeds 15 dB in the range of 1150–1360 nm. Compared to PbS-doped silica fiber, the PEDF has a gain improvement of 6.4–10.9 dB in O-band. In addition, the concentration of Pb and S in the PEDF core is significantly higher, and the size distribution of PbS nanoparticles is more concentrated in a narrow range. These factors may account for the enhanced gain characteristics of the PEDF. This work reveals the positive effect of co-doping Er3+ ions on the gain characteristics of the PEDF in O-band, and suggests an important research direction for the design of broadband amplifiers and light sources for optical communication with zero dispersion.

We investigate the spectral and amplification characteristics of Bi/Er co-doped fiber (BEDF) and Er-doped fiber (EDF), prepared by atomic layer deposition (ALD). BEDF features a noise figure (NF) below 5.2 dB, the bandwidth with NF less than 4 dB is approximately 23 nm (1560–1583 nm), and that with a gain exceeding 25 dB is approximately 42 nm (1525–1567 nm). The quantum conversion efficiency (QCE) of BEDF at 1550 nm is 72.1% at a pump power of 300 mW. The saturated output power of BEDF at 1550 nm is 21.4 dBm. Raman spectra indicate that the maximum phonon energy of BEDF is lower than that of EDF. The fluorescence lifetime of the BEDF is 11.64 ms, which is longer than that of the EDF. These results show that co-doping with Bi ions could increase the fluorescence lifetime of Er3+, reduce the NF, and improve the QCE and saturated output power. Therefore, this type of BEDF is a promising gain medium for optical amplifiers and lasers.

By examining the spectral and amplification characteristics of Er-doped silica fiber (EDSF) and Bi/Er co-doped silica fiber (BEDSF), an active doped silica fiber with broadband- and flat-gain is investigated. Results show that the bandwidth of BEDSF with a gain greater than 20 dB is approximately 50 nm. Moreover, in the entire C-band, the gain of BEDSF exceeds 26 dB with a fluctuation range of approximately 2 dB. The excellent performance may mainly come from the role of bismuth ions. Further analysis demonstrates that the emission and gain cross-sections are enhanced, the bandwidth is broadened, and the flatness is also optimized by co-doping Bi ions. The fluorescence lifetime of Er3+ is lengthened by 1.82 ms, illustrating that there may exist energy transfer from Bi-related active centers to Er3+. The results indicate that the proposed BEDSF has significant potential application in optical fiber amplifiers, lasers, sensors, and so on.

In this paper, an Ag nanoparticles (AgNPs) modified multimode fiber (MMF) SERS probe prepared based on sol self-assembly method is proposed and fabricated. Different fiber SERS probes (AgNPs-MMF-x, x is the self-assembly time) are obtained by adjusting the self-assembly time. Using rhodamine 6G (R6G) solution as the probe molecule, the far-end performances of the prepared fiber SERS probe are studied, and the AgNPs-MMF-30 probe with obvious advantages in SERS performance is obtained. The limit of detection (LOD) for R6G is as low as 10−9 M, demonstrating the high sensitivity of AgNPs-MMF-30 probe. The enhancement factor (EF) of AgNPs-MMF-30 probe to 10−7 M R6G is about 1.36 × 108. In addition, the AgNPs-MMF-30 probe has an outstanding reproducibility across the entire area with the maximum value of relative standard deviation (RSD) of less than 10.94%. The AgNPs-MMF-30 probe exhibit a long-term stability regarding Raman enhancement of up to 35 days. Importantly, the high-performance AgNPs-MMF-30 probe is further applied as a highly sensitive SERS platform for the trace detection of antibiotic in milk. The fiber SERS probe has the characteristics of fast, effective, remote real-time detection and so on, so it has great potential application in biochemical sensing and food security.

The magneto-refractive properties of Er/Yb co-doped silica fiber (EYDF) are important in magnetic field sensing. Here, we proposed a theoretical calculation model of the EYDF using density functional theory (DFT) and demonstrated it by an interferometric digital hologram magneto-refractive measurement system. The calculation results show that the fiber material, doped with Er/Yb atoms, has a large net spin and asymmetric spin distribution, which enables the elements to play an important role in the magnetic characteristics of the material. The experimental results show that the refractive index of the fiber decreases linearly with the increase of the magnetic field. The sensitivity of EYDF is 3.8279 × 10-5 RIU/Gs and is two orders of magnitude higher than that of single-mode fiber which is confirmed by the theoretical calculation. It demonstrated that the EYDF has advantages and potential of high sensitivity, miniaturization, and easy integration for magnetic field detection in harsh environments.

We report a magnetic field sensor based on an optofluidic microbottle resonator (OFMBR) with whispering gallery mode (WGM) strongly confined in the axial direction, with the hollow core inherently easy to infiltrate the magnetic fluid. The device is simply fabricated along a silica capillary through a fusing splicer. And the influence of number of discharges on the size of the device is analyzed according to the state equation of ideal gas, which is verified by experimental results. In the magnetic field range from the critical value (40 Gs) to the saturated value (300 Gs), the resonant wavelength shifts linearly with the increase of magnetic field strength, with a sensitivity of 8.45 pm/Gs demonstrated, based on the axial confined mode of OFMBR with a Q-factor of 1.28 × 106. This sensor possesses advantages of simple structure, easy fabrication process, and compact size for magnetic field sensing.