We demonstrate a novel fiber Bragg grating (FBG) temperature sensor based on lead sulfide (PbS)-doped silica optical fiber, prepared by atomic layer deposition (ALD) doping technique. The FBGs are fabricated using the phase mask method, without hydrogen loading. The temperature sensitivity of the FBG-PbS is found to be ~19 pm/°C within 20-150 °C, showing great linearity and repeatability. It is increased by approximately 60% compared to the temperature sensitivity of FBG in standard single mode fiber (SMF). Furthermore, the temperature characteristics of PbS-doped silica optical fiber are investigated. The thermal expansion coefficient and thermal-optic coefficient of PbS-doped silica fiber are $6.3 \times 10^{-7}$ and $1.23 \times 10^{-5}$ /°C, respectively. Moreover, the thermal-optic coefficient value of the PbS-doped silica optical fiber is nearly one order of magnitude higher than that of SMF. Therefore, the FBG based on PbS-doped silica optical fiber appears to be very attractive for the temperature sensing fields.

We have demonstrated an all-fiber high-order circularly polarized (CP) OAM modes (de)multiplexing system based on second-order mode selective couplers (SMSCs). Such SMSCs combining standard single mode fiber (SMF) and ring core fiber (RCF) are fabricated by a fusing and pulling technique, in which the RCF supports second-order vector modes $\rm (HE_{31} and EH_{11})$ . During a pulling process, the $\rm HE_{31} and EH_{11}$ modes could be excited along the coupling region through evanescent wave interaction. By adjusting the polarization states, the excited second-order modes are transformed into two sets of second-order circularly polarized OAM $\rm (CP-OAM_{\pm 2})$ modes and then transmit along the RCF. The second-order $\rm CP-OAM_{\pm 2}$ modes, carrying a 2.95-Gb/s orthogonal frequency division multiplexing (OFDM) signals filled with the 16-level quadrature amplitude modulation (16-QAM) signals, are successfully (de)multiplexed and propagated over a 3.7-km RCF. The experimental investigations show that the developed system to multiplex and transmit $\rm CP-OAM_{\pm 2}$ can achieve forward error correction (FEC) threshold that the received optical power is larger than -13 dBm. The obtained results show that the OAM modes can be generated, (de)multiplexed, and effectively transmitted in the RCF with favorable performance by the designed SMSCs.

An optical fiber sensor for simultaneous measurement of relative humidity (RH) and temperature is proposed, which is constructed by sandwiching one section of hollow core Bragg fiber (HCBF) between two sections of single mode fiber (SMF). The ultrathin ZnO film is coated on the outer surface of HCBF as humidity-sensitive material. The dips in the transmission spectrum caused by different anti-resonant (AR) modes of HCBF have different sensitivities to the RH and temperature, and then the simultaneous measurement of above two parameters can be realized by solving a cross matrix. For the two dips monitored in the experiments, the sensitivities of the proposed sensor to RH are 0.7 pm/%RH and 16.95 pm/%RH in the range of 46–73 %RH, and the sensitivities to temperature are 25 pm/°C and 26.8 pm/°C in the range of 20-60 °C, respectively. Taking advantage of compact structure, good stability, easy fabrication and the proposed sensor exhibits great potential application in fields of chemical sensors and biochemical detection.

The localized overheat is detrimental for the performance and lifetime of devices, especially in high-power, wide-bandgap semiconductor devices. But highly precise thermal characterization methods of the micro-nano regions within electronic devices remain challenging because of limitations in spatial resolution, electromagnetic interference and other factors. To address this challenge, we present a fluorescence thermometry utilizing a near-field fiber optic probe with quantum dots. Temperature-sensitive quantum dots modified on the probe tip as the nano-sensors provide excellent fluorescence stability and superior electromagnetic compatibility. The probe exchanges heat with the micro-nano scale hot spot on the sample surface and achieves thermal imaging based on the operating principle of scanning probe microscopy. The effective sensing area is minimized to nanoscale because of an aperture on the probe tip, achieving high detection spatial resolution. Using the probe with a sensitivity of 0.11 nm/°C, we investigated temperature difference of different-sized hot spots. The probe also effectively characterized the in-situ temperature distribution of an Au bonding wires with current flow inside, demonstrating its real-time monitoring capability for electronic devices. This innovative tool provides significant promise for performance assessment and failure analysis in electronic devices.

In this work, a cylindrical vector beams-based magnetic field sensor was proposed and demonstrated by using an yttrium iron garnet (YIG) crystal as the magneto-optical medium. The first-order cylindrical vector beam transmitted through a linear polarizer behind the YIG becomes a two-petal patterned light. When its polarization was rotated by the Faraday effect, the double petal pattern rotated accordingly. A slit was then used for filtering the transmitted patterned light, which was detected by a photodiode. The results showed that it could provide adjustable sensitivity up to 0.147%/mT within a range from $0.680~\mu $ T to 150mT. This work provides a high bandwidth and high sensitivity cylindrical vector beam magnetic field measurement technique which has potential applications in the field of alternating magnetic field measurements.

In this paper, we have proposed a novel type of fiber amplifier by filling the PbS semiconductor quantum dots into the holes of photonic crystal fibers (PCFs) for the first time. Based on simulation results, we have found that the loss of PCF filled with PbS is slightly increased compared with the one without PbS at wavelength of 1310 nm. Furthermore, we have successfully fabricated the PbS-filled PCF with selective air-hole cladding by a new perfusion technique that can optimize the overall loss.