We would like to continue the discussion of specific features of light leakage in the negative curvature hollow core fibers (NCHCFs). In our previous work, it was shown that consideration of the transverse Poynting vector component of air core modes in the vicinity of core–cladding boundary wall and its streamlines is of great importance for understanding light localization mechanism in NCHCFs. Using a simple model of a capillary with the azimuthally periodic distribution of the refractive index in the capillary wall, we demonstrate that the transverse Poynting vector component behavior is similar to that of NCHCFs. We also consider the impact of a supporting tube on light leakage in NCHCFs.
In this paper we consider a new type of hollow core microstructured optical fibers (HC MOFs) so called negative curvature hollow core fibers (NCHCFs). NCHCFs are known as hollow core fibers which allow to transmit a light under extremely high material loss of the cladding material. Such unique property of NCHCFs is due to the fact that their guiding mechanism is different from the guiding mechanisms in hollow core photonic crystal fibers (HC PCFs) and hollow core Bragg fibers (HC BFs). The two main factors which determine the guiding properties of NCHCFs are the ‘negative curvature’ (in a more general case, an alternating curvature) of the core – cladding boundary and the density of electromagnetic states of the cladding. It will be shown that the ‘negative curvature’ of the core – cladding boundary determines the type of interference which can lead to strong light localization in the air core. The interference which leads to air core mode formation in HC PCFs or HC BFs can be considered in terms of a linear momentum transfer by the photonic crystal cladding to the air core modes. In the case of NCHCFs the air core mode formation can be considered in terms of an azimuthal momentum transfer by the core – cladding boundary with an alternating curvature to the air core modes. The fabrication process of NCHCFs and several potential applications of NCHCFs in medicine, sensing and high power delivery are discussed.
Photonic bandgap Bragg fibers are promising for designing
large-mode-area structures owing to their high bend
immunity. However, at a large core diameter, filtering of high-order modes (mainly, the LP11 mode) becomes difficult,
because the propagation constant of such modes is close to that of the fundamental LP01 mode.
In this paper, we demonstrate the possibility to suppress high-order modes in Bragg fibers by introducing low-index
inclusions into the Bragg fiber core. Numerical analysis shows that an appropriate choice of the position and types of
such inclusions allows one to increase the LP11 mode radiation loss without increasing the optical loss of the fundamental
LP01 mode. The Bragg fiber with two B-doped and two
F-doped rods in the core was fabricated and studied. The
fundamental LP01 mode at 1064 nm had a mode-field area of about 340μm2 and an optical loss below 0.2 dB/m at a
bending radius of 15 cm. The LP11 mode was not observed in both bent and straight fibers at this wavelength. Only the
LP21 mode was detected in a straight fiber; however, it was completely suppressed after propagating a length of 60 cm in
a fiber bent with a radius <50 cm.
Prospects of fabrication of solid-core photonic bandgap fibers with a large mode area (LMA) are discussed. Properties
of solid-core photonic bandgap fibers with a small ratio of the cladding element diameter d to the distance Λ between
neighboring cladding elements are studied. The range of fiber parameters at which the fiber is single-mode over the
fundamental band gap is found.
The propagation properties of microstructured optical fibers useful for sensing applications are reviewed. The interaction between light and sample can reach 95 % in singlemode hollow core fibers and examples of structures exhibiting such large overlap ratios are described. The generation of 300 nm and 700 nm flat continua of visible and IR light in a single highly nonlinear holey fiber, well suited for the detection of biological species by spectroscopy, is reported. The low temperature sensitivity of long period gratings and of the birefringence in holey fibers is attractive for sensors operating in varying environmental conditions.
We present a detailed analysis of the effect of volumetric and surface inhomogeneities as a source of quality-factor limitation and intracavity resonant backscattering in optical microsphere cavities of fused silica. Intrinsic scattering in microspheres is shown to be significantly inhibited as compared to standard Rayleigh scattering in the bulk material. This reassessment of fundamental losses indicates that Q-factors substantially exceeding the previously expected limit of approximately 1011 can be obtained in microspheres, as soon as surface hydration is prevented. The intracavity backscattering is analyzed as a source of whispering-gallery mode splitting and resonant optical feedback in presence of a mode-matched travelling- wave coupler.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.