A temperature sensor with high sensitivity based on a tapered optical fiber with Al2O3 nanofilm by atomic layer deposition (ALD) technology is presented. Attributed to the high refractive index Al2O3 nanofilm overlay, an asymmetry Fabry-Perot interferometer is formed along the tapered fiber. Based on the ray-optic analysis, the resonant dip in the interference transmission spectrum depends on the phase delay variation induced by the Goos-Hänchen shift at the nanofilm-coating interface. As a result, the interference transmission spectrum shows good sensitivity to the change of surrounding refractive index. In this work, a temperature-sensitive silicone gel is coated around the fiber taper with Al2O3 nanofilm to realize a high sensitivity temperature sensor. The high sensitivity of 2.44 nm/°C is obtained.
A Pb/Al codoped silica fibers were fabricated using atomic layer deposition (ALD) technique in combination with modified chemical vapor deposition (MCVD). PbO and Al2O3 were induced into fiber core area by ALD. Faraday Effect of Pb/Al codoped silica fiber (PADF) was investigated for current sensor. Its Verdet Constant with 1 mm pitch was larger than 12% that of single mode fiber (SMF). It is very important for fiber-optic gyroscope and fiber-optic current sensors to optimize fabrication and design optical fibers, and to obtain relatively good magneto-optic sensitivity of optical fiber. This can be improved by Pb/Al codoped materials.
The physical characteristics and optical properties of PbS nanoclusters are investigated by using density functional theory (DFT) of first-principles. Microstructure models of (PbS)n (n=1-9) nanoclusters and bulk materials are built on Materials Studio platform, and its energy band structures, highest occupied molecular orbital-lowest unoccupied molecular orbital gap (HOMO-LUMO gap), density of state (DOS), and optical properties are calculated, respectively. Compared to PbS bulk materials, PbS nanoclusters show a discrete energy gap as well as the DOS, because of the quantum confinement effect. It is interesting that the HOMO-LUMO gap of (PbS)n (n=1-9) shows oscillates with the increasing of the n number. However, when its size is large enough, the HOMO-LUMO gap is gradually decrease with the increasing of size (>27 atoms). And, the HOMO-LUMO gap of PbS nanoclusters of different sizes is range from 2.575 to 0.58 eV, which covers the low loss communication band of optical communication. In addition, PbS nanomaterials (NMs) with small size are synthesized by using oleylamine as ligands. Sizes of PbS NMs can be accurately controlled through control of the reaction time as well as the growth temperature. The photoluminescence (PL) spectra show strong size dependence, which is large red shift with increasing size of the NMs. This trend is basically in agreement with the theoretical calculation above. Moreover, transmission electron microscopy (TEM) further reveals the morphology of PbS NMs. PbS NMs can be used in optical fiber amplifiers and fiber lasers because of its unique optical properties in optical communication bands.
Magneto-optical fiber plays an important role in magneto-optical devices. The fiber has larger Verdet constant will lead to a larger Faraday rotation per unit length fiber and applied field. In order to increase the magneto-optical characteristic, especially the Verdet constant of photonic crystal fiber, a magneto-optical fiber device based on combination of the magnetic fluid and the tunable photonic bandgap effect of photonic crystal fiber is proposed. The magnetic fluid is filled into the air holes of the cladding layer in the photonic crystal fiber using a new air pressure-filled method. Because the magnetic fluid prepared in this experiment has higher refractive index (>1.45), and is filled into the air-holes of photonic crystal fiber, as a result, the index guiding fiber is converted into photonic bandgap fiber. A magneto-optic system based on the Stokes polarization parameters method is designed which could analyze the Faraday effect. The corresponding Faraday rotation could be measured in the external magnetic field with different magnetic intensity by this magneto-optic system. The Faraday rotation of the photonic crystal fiber filled with magnetic fluid is approximately 5 times than that of the single mode optical fiber. The proposed magneto-optical fiber device takes full advantage of the ultrahigh sensitivity characteristic of photonic bandgap fiber and the large Verdet constant of magneto-optical fiber, can be used for high sensitive magnetic field sensor, magneto-optical switch, and magneto-optical modulator, etc.
Influence of spin manufacturing process on properties of the spun single mode fiber is investigated, a unidirectional spinning preform during the drawing process. The drawing speed constant is 1 m/min. The results show that pitch of the spun fiber exists; that mode field diameter (MFD) is obviously smaller; that cutoff wavelength and polarization mode dispersion (PMD) are decreased significantly, and then the loss is increased significantly when the spun fiber pitch is lower than 1.5 mm. It is very important for the fiber-optic gyroscope and fiber-optic current sensors to optimize spinning design to obtain relatively good spun fibers.
Radiation-induced transmission loss in Low Water Peak Single Mode (LWPSM) fiber has been investigated. Formation
and conversion processes of defect centers also have been proposed using electron spin resonance in the fiber irradiated
with gamma rays. When the irradiation dose is low, Germanium electron center (GEC) and self-trapped hole center
(STH) occur. With the increase of dose, E’ centers (Si and Ge) and nonbridge oxygen hole centers (NBOHCs) generate.
With the help of thermal-bleaching or photo-bleaching, the radiation-induced loss of pre-irradiation optical fiber can be
reduced effectively. The obtain results also have been analyzed in detail.
The Faraday magneto-optical effect of optical fiber has many applications in monitoring magnetic field and electric current. When a linearly polarized light propagates in the direction of a magnetic field, the plane of polarization will rotate linearly proportional to the strength of the applied magnetic field, which following the relationship of θF =VBl. θF is the Faraday rotation angle, which is proportional to the magnetic flux density B and the Verdet constant V .
However, when the optical fiber contains the effect of linear birefringence, the detection of Faraday rotation angle will depend on the line birefringence. In order to determine the Verdet constant of an optical fiber under a linear birefringence, the fiber birefringence needs to be accurately measured. In this work, a model is applied to analyze the polarization properties of an optical fiber by using the Jones matrix method. A measurement system based on the lock-in amplifier technology is designed to test the Verdet constant and the birefringence of optical fiber. The magnetic field is produced by a solenoid with a DC current. A tunable laser is intensity modulated with a motorized rotating chopper. The actuator supplies a signal as the phase-locked synchronization reference to the signal of the lock-in amplifier. The measurement accuracy is analyzed and the sensitivity of the system is optimized. In this measurement system, the Verdet constant of the SMF-28 fiber was measured to be 0.56±0.02 rad/T·m at 1550nm. This setup is well suitable for measuring the high signal-to-noise ratio (SNR) sensitivity for lock-in amplifier at a low magnetic field strength.
Infrared spectra of optical fiber cladding materials have been investigated by the irradiating treatment, and the
quenching and annealing process with different temperature. The results show that, with the method of quenching firstly,
the 1100 cm-1 peak in the IR spectrum of cladding materials changes dramatically, which may attribute to the quenching
process, corrected the fictive temperature and induced structural disorder. And then, the irradiation process induces
defects. Finally annealing process can make the material become more stable, but the intensity and shape of 1100 cm-1
peak no change remarkably. This result shows that annealing process repaired the structural disorder induced by
quenching process and the defects induced by irradiated.
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.
The structures and optical properties of (PbS)n cluster in silica optical fiber material are investigated. The microstructures models of (PbS)n (n=1-4) and PbS-(SiO2)n (n=1-6) have been built and calculated by Gaussian-03 software using density functional theory with the B3LYP level. The gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) is also calculated for microstructures. Compared with the (PbS)n clusters and (SiO2)n clusters, The HOMO-LUMO gaps of (PbS)n clusters combined with (SiO2)n clusters make a big difference. The geometry structures of (PbS)n-(SiO2)4 (n=2-4) clusters are calculated by using the singles configuration interaction (CIS) method. The calculation results show that the excitation energies of (PbS)n-(SiO2)4 clusters changed as the sizes or the structures are changed. The PbS-doped silica optical fiber is fabricated, and the optical properties are measured to compare with the theoretical results.
Defect centers play a major role in the radiation-induced transmission loss for silica optical fibers. We have investigated
characteristics of the best known defect centers E' in silica optical fiber material irradiated with γ ray at room temperature,
and measured by using electron spin resonance (ESR) and spectrophotometer. The results show that the defect
concentrations increase linearly with radiation doses from 1kGy to 50kGy. We have established the mechanism models
of radiation induced defect centers' formation. We have also studied the influences of thermal annealing on defect centers.
The radiation induced defect centers can be efficiently decreased by thermal annealing. Particularly, the defect
concentration is less than the initial one when the temperature of thermal annealing is over 500°C for our silica samples.
These phenomena can also be explained by the optical absorption spectra we have obtained.
Reducing the radiation-induced transmission loss in low water peak single mode fiber (LWP SMF) has been investigated
by using photo-bleaching method with 980nm pump light source and using thermal-bleaching method with temperature
control system. The results show that the radiation-induced loss of pre-irradiation optical fiber can be reduced effectively
with the help of photo-bleaching or thermal-bleaching. Although the effort of photo-bleaching is not as significant as
thermal-bleaching, by using photo-bleaching method, the loss of fiber caused by radiation-induced defects can be
reduced best up to 49% at 1310nm and 28% at 1550nm in low
pre-irradiation condition, the coating of the fiber are not
destroyed, and the rehabilitating time is just several hours, while self-annealing usually costs months' time. What's more,
the typical high power LASER for photo-bleaching can be 980nm pump Laser Diode, which is very accessible.