Yanhua Dong

Refractive index sensitivity of nano-film coated long-period fiber gratings.

We demonstrate the fabrication of long-period fiber gratings (LPFGs) coated with high index nano-film using the atomic layer deposition (ALD) technology. Higher index sensitivity can be achieved in the transition region of the coated LPFGs. For the LPFG coated by nano-film with a thickness of 100 nm, the high index sensitivity of 3000 nm/RIU and the expanded index sensitive range are obtained. The grating contrast of the over-coupled LPFGs and conventional LPFGs are measured and the over-coupled gratings are found to have a higher contrast in the transition region. The cladding modes transition is observed experimentally with increasing surrounding index using an infrared camera. The theoretical model of the hybrid modes in four-layer cylindrical waveguide is proposed for numerical simulation. The experimental results are well consistent with theoretical analysis.

High sensitivity refractive index sensor based on adiabatic tapered optical fiber deposited with nanofilm by ALD.

Atomic layer deposition (ALD) technology is introduced to fabricate a high sensitivity refractive index sensor based on an adiabatic tapered optical fiber. Different thickness of Al2O3 nanofilm is coated around fiber taper precisely and uniformly under different deposition cycles. Attributed to the high refractive index of the Al2O3 nanofilm, an asymmetry Fabry-Perot like interferometer is constructed along the fiber taper. Based on the ray-optic analysis, total internal reflection happens on the nanofilm-surrounding interface. With the ambient refractive index changing, the phase delay induced by the Goos-Hänchen shift is changed. Correspondingly, the transmission resonant spectrum shifts, which can be utilized for realizing high sensitivity sensor. The high sensitivity sensor with 6008 nm/RIU is demonstrated by depositing 3000 layers Al2O3 nanofilm as the ambient refractive index is close to 1.33. This high sensitivity refractive index sensor is expected to have wide applications in biochemical sensors.

Refractive index sensitivity enhancement of optical fiber cladding mode by depositing nanofilm via ALD technology

The atomic layer deposition (ALD) technology is introduced to enhance the sensitivity of optical fiber cladding mode to surrounding refractive index (SRI) variation. The highly uniform Al2O nanofilm was deposited around the double cladding fiber (DCF) which presents cladding mode resonant feature. With the high refractive index coating, the cladding mode resonant spectrum was tuned. And the sensitivity enhancement for SRI sensor was demonstrated. Through adjusting the deposition cycles, a maximum sensitivity of 723 nm/RIU was demonstrated in the DCF with 2500 deposition cycles at the SRI of 1.34. Based on the analysis of cladding modes reorganization, the cladding modes transition of the coated DCF was investigated theoretically. With the high performance nanofilm coating, the proposed SRI sensor is expected to have wide applications in chemical sensors and biosensors.

Temperature Sensitivity Enhancement of the Nano-Film Coated Long-Period Fiber Gratings

We present a new method to improve the temperature sensitivity of the long-period fiber gratings (LPFGs). The atomic layer deposition technology is used to deposit Al2O3 nano-film on the LPFG written in the conventional single-mode fiber. Then, the coated LPFG is packaged by the polymer material. The theoretical model of the hybrid modes in the four-layer cylindrical waveguide is proposed for a numerical analysis. Experimental results show that the temperature sensitivity up to 0.77 nm/°C is achieved for the HE1,10 mode of the LPFG coated with 200-nm nano-film and then packaged by the silicone rubber. The temperature sensitivity is almost one order magnitude larger than that of the bare LPFG. Various physical effects for the temperature sensitivity enhancement are investigated theoretically and experimentally. The experimental results are well consistent with a theoretical analysis.

Radiation-induced photoluminescence enhancement of Bi/Al-codoped silica optical fibers via atomic layer deposition.

The radiation-induced photoluminescence (PL) properties of Bi/Al-codoped silica optical fibers were investigated. The Bi/Al-related materials were doped into fiber core via atomic layer deposition. The pristine fiber samples were irradiated with different doses, and its absorption and PL properties were studied. A new absorption peak appeared at approximately 580 nm, and the intensity of absorption peaks is increased with the increasing of radiation doses. When the fiber samples were excited with a 532 nm pump, the intensity of the near infrared fluorescence decreased lightly. However, when the fiber samples were excited with a 980 nm pump the intensity of the fluorescence increased significantly with the increase of radiation doses (0-2.0 kGy). The intensity of fluorescence decreased when the radiation doses were increased up to 3.0 kGy. furthermore, the fluorescence intensity of the 1410 nm band increased much more than that the 1150 nm band. In addition, the microstructural characteristics of the Bi/Al-codoped silica optical fibers were analyzed using electron spin resonance (ESR). Many radiation-induced defect centers were present, and the intensity of the ESR signals also increased with the increase of radiation doses. The photoluminescence properties and microstructural characteristics were related in the radiated Bi-related silica optical fibers. A possible underlying mechanism for the radiation-induced photoluminescence enhancement process in the Bi/Al-doped silica fiber is discussed.

Formation and photoluminescence property of PbS quantum dots in silica optical fiber based on atomic layer deposition

The PbS Quantum Dots (QDs)-doped silica optical fiber is fabricated using atomic layer deposition (ALD) technique in combination with modified chemical vapor deposition (MCVD) technology. PbS materials are introduced into the fiber core and then formed to QDs in the optical fiber materials during the preparation process. Its structure features and optical properties are investigated. The element distribution and stoichiometry of the core materials are revealed by μ-X-ray absorption near edge structure (μ-XANES), μ-X-ray fluorescent (μ-XRF) and energy dispersive spectrometer (EDS) analysis. The experiment results indicate that PbS QDs are distributed at the region between core and cladding layers with the concentration about 0.11 mol%. High resolution transmission electron microscopy (HRTEM) further reveals the dispersion of PbS QDs is uniform and its nanocrystalline size is about 2-6 nm. This is basically in agreement with the evolution results with effective-mass method. Additionally, PbS QDs-doped optical fiber pumped with 980 nm exhibits photoluminescence property in the 1050-1350 nm range. The special doping fibers will show application potential in optical fiber amplifiers, fiber lasers and optical sensing.

Bismuth-doped silica fiber fabricated by atomic layer deposition doping technique

We fabricated Bi-doped silica fiber by atomic layer deposition doping technique. The refractive index difference of fiber is 0.58 %. The absorption peak is at 500 nm, 700 nm, 800 nm, and 1000 nm. The fluorescence peak is 1130 nm.

Measurements of the magneto-optical properties of PbS-doped silica optical fiber

The Verdet constants of PbS-doped silica optical fiber and single mode fiber (SMF-28e) have been investigated based on a magneto-optical effect measurement system at wavelengths between 660 and 1550 nm. The Verdet constant of PbS-doped fiber is 3.17 rad/Tm, 31.5% larger than that of SMF at 660 nm. The PbS-doped silica optical fiber can become a promising material for Faraday rotator.

Thermal induced birefringence of the PbS doped silica fiber

A PbS doped fiber was proposed and fabricated for temperature sensor application. The sensitivity of the fiber birefringence to temperature is 0.068 rad/K/m which is 8 times larger than SMF.

Absorption spectrum of the PbS-doped silica fibers fabricated by ALD and MCVD

The technique of atomic layer deposition (ALD) has been introduced to fabricate PbS-doped silica fibers, whose absorption peaks are discovered to be shifted from 1230 nm to 920 nm when the number of ALD deposition cycles varies from 80 to 30 during optical fiber preform fabrication. This is explained by suggesting that the PbS doped in fiber are under the 3D quantum confinement, i.e., quantum dots (QDs). An effective-mass approximat ion of the PbS QDs ’ sizes is then made to show the shift of absorption peaks can be attributed to the change of size distribution of these dots.