A sapphire fiber high temperature sensor based on Fabry-Perot interference was studied in the paper. A sapphire wafer served as the Fabry-Perot cavity was fixed to the end face of the sapphire fiber. The sensor was encapsulated in an alumina ceramic tube-ceramic sleeve structure to improve structural stability. Experiment results showed the sensor had a wide temperature measurement range of 25 °C-1550 °C. The temperature sensitivity reached 32.5 pm/°C at 1550 °C. Furthermore, the temperature was demodulated from the interference spectrum through fast Fourier transform algorithm. It was concluded that the sapphire fiber sensor with advantages of small size, good stability and a wide range of temperature measurement is very promising for measuring high temperature.

In this paper, we report an optical frequency comb (OFC) generated in a whispering-gallery-mode microbottle resonator, and present a convenient and simple method for adjustment of the zero dispersion wavelength (ZDW). The ZDW tunability of the microbottle resonator realized by exciting modes with different axial mode numbers is predicted theoretically and demonstrated experimentally by changing the coupling position of a tapered fiber. Cascaded four-wave mixing (FWM)-based frequency combs are investigated by pumping the resonator in different dispersion regimes. The results show that the OFC based on degenerated FWM could be generated under the anomalous dispersion, while Raman or Raman-assisted OFC are obtained in the normal dispersion regime.

An optical fiber immunosensor with a low detection limit based on plasmon coupling enhancement is proposed for detecting human immunoglobulin G (IgG). Graphene oxide (GO)-gold nanorod composites are synthesized and modified onto a photonic crystal fiber (PCF) surface coated with a Au film. GO, as a biosensitive layer, is used to decorate the gold nanorods and concentrate target molecules. The experimental result indicates that the refractive index sensitivity is drastically enhanced to 22248 nm/RIU because of plasmon coupling. Correspondingly, the human IgG detection limit decreases to 6 ng/mL. Moreover, the PCF is insensitive to temperature fluctuation, which can further reduce the measurement error.

A novel sensing peak identification method for high accuracy refractive index (RI) sensing is proposed. The implementation takes the intensity of interference maximum as the characteristic to distinguish interference peaks, tracking the sensing peak continually during a RI changes, with high measurement accuracy and simple computation. To verify the effect of the method, the extrinsic Fabry–Perot interferometer (EFPI) sensor has been fabricated using the large lateral offset splicing technique. In the RI range from 1.346 to 1.388, the measurement range of the EFPI with the proposed method reaches at least 6 times larger than that of EFPI with the wavelength tracking method and the largest measurement error is −4.47 × 10⁻⁴. The EFPI refractive index (RI) sensor identified the sensing peak is believed to play an important role in RI, concentration and density sensing, etc., for superior performance.

Whispering-gallery-mode (WGM) microresonators. reveal enormous potential applications in fields ranging from micro/nano-optics, integrated and quantum optics, to optical precision measurements. In this paper, we propose a novel cascaded WGM microresonator which is composed of two partially overlapped microbottle resonators. The distribution property of mode intensity and the variation characteristic of quality factors (Q factors) were analyzed theoretically, and demonstrated by evanescently exciting the microresonator with a tapered fiber at different axial positions. Based on the cascaded microbottle resonator, a stable add-drop filter was demonstrated, and the effective excitation properties of the modes in the microresonator were discussed for the first time. Due to the larger axial dimension, the proposed WGM microresonator could also find applications in strain sensors and time delay devices.