KEYWORDS: Multimode fibers, Temperature metrology, Distance measurement, Spatial resolution, Raman scattering, Data acquisition, Cladding, Signal attenuation, Raman spectroscopy, Refractive index
Raman distributed temperature sensing (RDTS) is widely used in many fields. The system configuration, devices, and data processing methods have been well studied and improved, but research on sensing fiber itself is rare. We design a multimode fiber for RDTS based on experimental results from a series of conventional multimode fibers. The optimized multimode fiber offers temperature sensing at a distance less than 10 km. It has a much larger nonlinear effect than conventional multimode fibers, so the spontaneous anti-stokes signal under the same optical input is 1.5 to ∼ 2.4 times higher. Its loss and dispersion within the wavelength range from 1400 to 1650 nm is acceptable. Therefore, under the same system configuration, a higher anti-stokes signal is received by the data acquisition card, which makes signal acquisition and processing easier and improves temperature sensitivity, accuracy, and resolution without sacrificing other characteristics, such as spatial resolution and measuring distance.
In this paper, we drew a 500 m-long PCF taper directly on the industry drawing tower. The fiber taper has a uniform
cross-section structure with OD from 170 μm to 70 μm, and demonstrates very good beam quality. The optical
attenuation of PCF taper was measured. The optical attenuation is ~5 dB/km near 1200 nm, but the water absorption
peak around 1400 nm and the attenuation beyond 1600 nm are still large. The zero dispersion wavelength (ZDW) was
calculated to be ~1090 nm at the taper input end, and shifted to ~870 nm at the taper output end. The PCF taper was
pumped with a picosecond laser source at wavelength of 1064 nm, and generated 200 mW output power of SC covering
from ~450 nm to 1600 nm.
A novel compact temperature sensor based on a fiber loop mirror (FLM) combined with an alcohol-filled highlybirefringent
photonic crystal fiber (HiBi-PCF) is proposed and experimentally demonstrated. The output of the FLM is
an interference spectrum with many dips, of which the resonant wavelengths are quite sensitive to temperature because
the interference of the FLM is sensitive to the optical path difference due to the refractive index change of the filled
alcohol. Experimental results show that the temperature sensitivity reaches up to 5.42nm/°C for a 6.3cm long alcoholfilled
PCF used in the FLM.
Temperature stability based on high Ge-doped fibre Bragg grating (FBG) is presented. A high Ge-doped photosensitive
fibre (PSF) used for writing FBG was manufactured. Temperature characteristic of the FBG from 20 to 300°C had been
researched. The transmission efficiency is about 75% at 300°C.
We have theoretically investigated the polarization properties of a single-mode photonic crystal fiber (PCF), which is
pulsed one-side by CO2 laser resulting in partial air-holes collapse and deformation. The CO2 laser micro-fabrication is a
common way in PCF post-processing, which is used widely both in writing fiber gratings on PCFs and making optical
components such as PCF polarizers. A series models with different valley depth which is due to the collapsed air-holes
have been simulated by using a full-vector finite-element method (FEM) with a perfectly matched layer (PML). The
theoretical results show that the deeper valley causes a larger insertion loss, at the same time, leading a larger
polarization dependence loss (PDL). This research provides an insight into the side-pulsed PCF as well as a guidance on
the experiment of CO2 laser micro-fabrication on PCFs.
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