In recent years, fiber sensors have the advantages of compact structure, anti-electromagnetic interference, anti-corrosion and remote monitoring when compare to the traditional sensors. Many technologies have been created to prepare all fiber sensors, such as long period gratings, fiber Bragg gratings, F-P interferometer. However, these fiber sensors are uselessness due to the complex structure, low sensitivity and high cost.

Quite recently, Doc. Xiongwei Hu, from Fiber Laser Technology Group (FLTG) Wuhan National Laboratory for Optoelectronics, explored the all fiber M-Z interferometer for high temperature sensing based on a hetero-structured cladding solid-core photonic bandgap fiber under the guidance of Prof. Nengli Dai, Jinyan Li, Luyun Yang. They designed and fabricated a hetero-structured cladding solid-core photonic bandgap fiber (HSCS-PBGF) which supports vibrant core mode and cladding mode transmission. Then they constructed an all fiber M-Z interference sensor by splicing single mode fiber at both ends of HCSC-PBGF without any other micromachining. The measurements show that the sensitivity of this fiber sensor is as high as 90 pm/°C when operating from room temperature to 1000 °C. Furthermore, the insertion is less than 1 dB, the fringe contrast reaches to 20 dB and the maximum dynamic range is larger than 200 nm. It is obvious that this all fiber sensor have great applicable prospect in fiber sensing with the advantages of compact structure, high sensitivity and cost-effective.

On September 9, 2016, this work entitled with “all fiber M-Z interferometer for high temperature sensing based on a hetero-structured cladding solid-core photonic bandgap fiber” has been published in Optics Express(Optics Express 24(19) 21693-21699 (2016) in the optical society of America (OSA). This work was financially supported by the National Natural Science Foundation of China (Grant No. 61378070,61575075,51672091).

Fig. 1. (a) The micrograph shows the cross section of the HCSC-PBGF. (b) Schematic diagram and operation of the MZI. (c)- (d) Microscopic images of the fusion splicing joints.

Fig. 2. (a) Transmission spectrum of the MZI with 10 cm long HCSC-PBGF. (b) Beam propagation simulation of the MZI at the wavelength of 1562.97 nm and 1587.26 nm, respectively.

Fig. 3 Interference spectrum of MZI with different lengths of HCSC-PBGF (L= 45 cm, 37cm, 22.5 cm).

Fig. 4. (a) The effective refractive indices of core mode and cladding mode. (b)-(c) The intensity profiles of core mode and cladding mode calculated by full-vector finite element. (d) Spatial frequency spectrum by taking the FFT for MZI with the length of HCSC-PBGF is 45 cm, 37 cm and 22.5 cm.

Fig. 5 (a) Response to high temperature for the HCSC-PBGF-based MZI. (b) Interference spectra at 29 °C, 200 °C, 400 °C, 600 °C, 800 °C, 1000 °C.