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.
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.
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.
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.
Normalized frequency, normalized propagation constant and asymmetry measure are introduced to the left-handed slab
waveguides. The dispersion relations expressed by normalized parameters are then derived. All the possible waveguide
configurations with the left handed materials as core, substrate, and cover are considered and divided into four cases.
Universal dispersion curves, and dispersion properties have been obtained analytically. It is found that guided mode
properties differ dramatically for these four cases. For some cases, fundamental mode does not exist. For some cases,
double degeneracy of modes appears. In one case, the first order mode only exists in a small frequency range, while in
another case the fundamental mode exists only in a small frequency range. Both TE and TM oscillating guided modes
In this paper, we present two new photonic crystal structures, which are composed of fractal Cantor multilayer with defects embedded in its middle. Optical transmission matrix method is used to calculating the transmittance and reflectance. Compared with general Cantor multilayer, we find these new structures have wider stopbands and show super narrow bands in the middle of wider stopbands. They can be served as super narrow bandpass filters. The pass band obtained can be less than 0.6nm near the infrared 1530 nm when there is a defect embedded in the cantor multilayer. The optical transmission in the center wavelength is higher than 99%. This means a very low insert loss. If there are three detected layers, three super narrow peaks can be found in the middle of the stopband. The center wavelengths are 1232.4 nm, 1372.8nm and 1538.3 nm, respectively. It is more superior to other kind narrow band filters. These kinds of photonic crystal super narrow band optical filters may find applications in super dense wavelength division multiplexing for optical communications and precise optical measurement.
In this paper, we present a novel cross section shape DCF. Truncated from a circular DCF, the inner cladding of this DCF is bounded by two equal angular spiral curves. By using the concept of mean transverse path between successive encounters of the core, we developed a new method to calculate the absorption efficiency per unit fiber length. For a spiral shape DCF with the largest radius R=100μm , radius of doped core r0=4μm , and the angle parameter of spiral curve θ=0.04 , we calculated the mean transverse path between successive encounters of the core lr=2903μm . The corresponding lc with other truncated shape cross section having the same cross sectional area is lc=3454μm . Final results show that the absorption efficiency η increases 16% for our spiral shape DCF.
In this paper, a novel chiral photonic crystal structure is presented. The formula of reflection coefficient of multi-layer chiral media is applied to dielectric-chiral photonic crystal structure, which is composed of thin chiral layers sandwiched by conventional media. To compare with previous literature, we consider the dielectric structure with alternate glass and GaAs layers. The power reflectance as a function of wavelength for this photonic crystal structure has been calculated. The results are in good agreement with that of Reference. However, our method is simpler. From these graphs, it is found that 100% reflectance is only in finite wavelength ranges, and reflection bandwidth is also small for conventional photonic crystal structure. For chiral photonic crystal, the results show that the chiral photonic band gap (PBG) structure gives nearly 100% reflections in the near-infrared region in addition to some parts of the visible region of the wavelengths. Therefore, it can be used as a broadband reflector and filter.
In this paper, the formula of reflection coefficient of multi-layer chiral media is derived by non-symmetric transmission-line method. Then, it is applied to 1-D chiral photonic crystal structure, which is composed of thin chiral layers sandwiched by air. The results show that it is difficult to obtain photonic band gap for general dielectric when the difference of two media refractive indices isn't large, and the reflection coefficient is small. With the increasing of the refractive index of the medium, reflection coefficient becomes gradually large, and reflection bandwidth basically keeps unchanged. These characteristics are agreed with results of theoretical analysis of photonic crystal. However, for chiral photonic crystal, although the refractive index of chiral layer is small, the wave spectrum obtained contains forbidden zones and the reflection coefficient from such a structure is found to be almost equal to 1, i.e., the wave is almost totally reflected through adjusting chiral parameter. Therefore it is easier to obtain an ideal photonic band gap.