Photonic crystal fibers (PCF) are excellent-performing fibers with flexible aperture design and has the advantages of high birefringence [1,2], large mode field area [3], low confinement loss and high sensitivity [4,5] Sensors based on PCF have attracted the attention of researchers in the field of sensing because of their excellent sensing ability, especially in temperature sensing applications, which can solve some of the limitations of traditional fiber optic temperature sensors, such as the inability to ensure the polarization state of the fiber, loss and other shortcomings [[6], [7], [8]]. However, the temperature sensitivity of PCFs still needs to be improved. To solve this problem, the method of filling the air holes of PCF with temperature-sensitive materials is usually used to improve the temperature sensing ability of the device and to expand the application of PCFs in temperature sensors [9].

Currently, there are many methods to calculate the sensitivity of PCF-based temperature sensors, and the common methods are to calculate the sensitivity by measuring the peak shift of the interference spectrum affected by the thermal effect [10], and to measure the sensitivity of PCFs by the birefringence change of PCFs [[11], [12], [13]].

In 2022, Di et al. [14] designed two-core PCF by filling liquid crystal, and obtained the maximum sensitivity of −6.69 nm/°C at 30 °C. Gao et al. [15] used ethanol as filling material to design a photonic crystal refractive index temperature sensor, and obtained a sensitivity of −0.306 nm/°C in the range of 40–50 °C. However, the temperature sensitivity still has a large room for improvement, and the temperature detection range is small, which is not enough to meet the demand. Recently, PDMS (Poly-dimethylsiloxane) elastomer is a widely used material in the area of photonics and particularly in opto/microfluidics. It owns unique optical properties such as transparency for a wide range of wavelength, lower refractive index (around 1.41) than fused silica, negligible birefringence, minimal loss due to absorption. These properties combined with its low cost and ease fabrication procedure make PDMS a potential active material for sensing applications [16,17].

In this paper, we proposed a temperature sensor based on a birefringent PCF for temperature measurements from −20 °C to 20 °C. Firstly, we designed a petal-like PCF, which adopts the design idea of combining many circular apertures with two elliptical apertures, and uses silicon with high refractive index as the substrate to better bind the energy in the fiber core to reduce the confinement loss. By adjusting the ellipticity, the optimal PCF structure was obtained,and the PDMS was injected into the elliptical air apertures inside the PCF, which greatly improved the temperature sensitivity of the modified sensor up to 8.01 nm/°C. Meanwhile, the temperature detection range can also be adjusted according to the length of the sensing fiber, which greatly improves its application range in temperature detection.