Browsing by Subject "Photonic Band Gap"

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • Thumbnail Image
    ItemOpen Access
    Hollow core photonic bandgap fibers for medical applications
    (2009) Vural, Mert
    The design, fabrication and characterization of photonic band gap (PBG) based optical polymer fibers is discussed. Unlike conventional total internal reflection (TIR) fibers, used primarily in telecommunications, PBG fibers can be made hollow core and can be used to guide infrared radiation of any wavelength, a property known as wavelength scalability. Since the electromagnetic radiation is transmitted in the hollow core of the fiber, the intrinsic absorption of the fiber core as well as the insertion Fresnel losses at front and end faces are avoided, giving rise to extraordinarily high power densities to be delivered. The fiber production line includes material characterization, and the design of nanoscale quarter wavestacks using common thermoplastic polymers (poly ether sulphone and poly ether imide) and chalcogenide glasses (As2S3, As2Se3, Ge15As25Se15Te45). The fiber preform is fabricated using rolling mechanism of thermally evaporated chalcogenide glasses on large area polymers. Subsequently, the fiber preforms are thermally drawn to obtain nano-structured PBG fibers.Two different fibers are designed and produced, signifying wavelength scalability of the overall process, for the widely used holmium (Ho:YAG) and carbon dioxide (CO2) medical lasers. The transmission characteristics of the fibers proved that they can be used to safely deliver 15Wlaser power, along a 3 meter fiber with external diameter of 1.5 mm and hollow core diameter of 0.5 mm, corresponding to a laser power density of 1kW/cm2 with a loss of -10dB/m. The PBG fibers are expected to be widely used in high precision surgical laser for incision, photoablation and coagulation where infrared radiation is the radiation of choice for its superior laser-tissue interaction properties.
  • Thumbnail Image
    ItemOpen Access
    Negative refraction using true left-handed metamaterials
    (2004) Aydın, Koray
    Left-handed materials and negative refraction attracted a great amount of attention in recent years due to their unique physical properties. It is possible to obtain a left-handed material by combining a novel artificial structure (split ring resonator) and a wire structure periodically. We investigated the transmission and reflection properties of split ring resonators (SRR), wires and composite metamaterials consisting of SRR and wire structures. We have successfully demonstrated true left-handed behavior in free space with a high transmission peak (-1.2 dB). This is the highest transmission peak reported for a left-handed material. The left-handed transmission band coincides exactly with the region where both dielectric permittivity and magnetic permeability have negative values. We proposed and demonstrated a new method to distinguish the magnetic resonance of the SRR structures. We experimentally confirmed that composite metamaterial has a negative refractive index, at the frequencies where left-handed transmission takes place. Phase shift between consecutive numbers of layers of CMM is measured and phase velocity is shown to be negative at the relevant frequency range. Refractive index values obtained from the refraction experiments (-1.87) and the phase shift experiments (-1.78) are in good agreement.