Burak Temelkuran

Wavelength-scalable hollow optical fibres with large photonic bandgaps for CO 2 laser transmission

Conventional solid-core optical fibres require highly transparent materials. Such materials have been difficult to identify owing to the fundamental limitations associated with the propagation of light through solids, such as absorption, scattering and nonlinear effects. Hollow optical fibres offer the potential to minimize the dependence of light transmission on fibre material transparency. Here we report on the design and drawing of a hollow optical fibre lined with an interior omnidirectional dielectric mirror. Confinement of light in the hollow core is provided by the large photonic bandgaps established by the multiple alternating submicrometre-thick layers of a high-refractive-index glass and a low-refractive-index polymer. The fundamental and high-order transmission windows are determined by the layer dimensions and can be scaled from 0.75 to 10.6u2009µm in wavelength. Tens of metres of hollow photonic bandgap fibres for transmission of carbon dioxide laser light at 10.6u2009µm wavelength were drawn. The transmission losses are found to be less than 1.0u2009dBu2009m-1, orders of magnitude lower than those of the intrinsic fibre material, thus demonstrating that low attenuation can be achieved through structural design rather than high-transparency material selection.

Dielectric omnidirectional visible reflector.

We demonstrate the fabrication of an all-dielectric omnidirectional mirror for visible frequencies. The dielectric reflector consists of a stack of 19 alternating layers of tin (IV) sulfide and silica. Using a combination of thermal evaporation (for tin sulfide) and thick electron-beam evaporation (for silica), we have achieved a refractive-index contrast of 2.6/1.46 , one of the highest refractive-index contrasts demonstrated in one-dimensional photonic bandgap systems designed for the visible frequency range. The tin sulfide-silica material system developed allowed the formation of a broadband visible reflector with an omnidirectional range greater than 10%. Possible applications of the system include efficient reflectors, high-frequency waveguides for communications and power delivery, and high- Q cavities.

Low-loss infrared dielectric material system for broadband dual-range omnidirectional reflectivity

A material system for broadband thermal IR applications based on branched polyethylene and tellurium is introduced. This system exhibits low absorption losses from 3.5 to 35 microm , has a large index contrast, and is readily deposited as a thin film. These unique features were used to investigate the formation of an omnidirectional reflector that exhibits two distinct, broadband omnidirectional ranges at thermal wavelengths. Reflectivity measurements are presented that confirm the existence of two omnidirectional ranges in the solar atmospheric windows extending from 8 to 12 microm and from 4.5 to 5.5 microm . The measurements are in good agreement with simulations.

Gas Flow During Bronchoscopic Ablation Therapy Causes Gas Emboli to the Heart: A Comparative Animal Study

BACKGROUNDnThermal ablation is one of the most commonly used modalities to treat central airway obstruction. Both laser and argon plasma coagulation (APC) have been reported to cause gas emboli and cardiac arrest. We sought to determine whether bronchoscopic ablation therapy can result in systemic gas emboli, correlate their presence with the rate of gas flow, and establish whether a zero-flow (ZF) modality would result in the significant reduction or elimination of emboli.nnnMETHODSnCO(2) laser delivered through a photonic bandgap fiber (PBF) and APC were applied in the trachea and mainstem bronchi of six anesthetized sheep at varying dosages and gas flow rates. Direct epicardial echocardiography was used to obtain a four-chamber view and detect gas emboli.nnnRESULTSnThe presence of gas flow accompanying APC and the CO(2) laser with forward flow correlated significantly with the appearance of gas bubbles in the atria. A definite dose response was observed between the gas flow rate and the number of bubbles seen. When the CO(2) laser was delivered through a PBF with ZF to the trachea or bronchi, no bubbles were observed.nnnCONCLUSIONnBronchoscopic thermal ablation therapy using gas flow is associated with gas emboli in a dose-dependent fashion. The use of the flexible PBF with ZF is not associated with the development of gas emboli. Further study is required to determine whether a clinically safe threshold of gas emboli exists, and the relationships among the pathologic depth of tissue destruction, gas flow, pulse duration, and the development of gas emboli.

OmniGuide photonic bandgap fibers for flexible delivery of CO2 laser energy for laryngeal and airway surgery

The CO2 laser is the most widely used laser in laryngology, offering very precise cutting, predictable depth of penetration, and minimal collateral damage due to the efficient absorption of CO2 laser by water. Surgical applications of CO2 laser in microlaryngoscopy include removal of benign lesions and early-stage laryngeal cancer. A Transoral Laser Microsurgery (TLM) approach is routinely employed for treatment of laryngeal cancer; however, the role of TLM in advanced malignant lesions remains controversial. The main limiting factor of TLM is the restrictive exposure of the endoscopes combined with the limited cutting ability offered by the existing micromanipulator, enabling cutting only along the straight line-of-sight axis. A flexible fiber delivery system offering a very high quality output beam can offer tangential cutting and can therefore significantly enhance the existing surgical capabilities. Moreover, a flexible fiber for CO2 laser delivery can be used for treatment of benign conditions through flexible endoscopy in an office setting using local anesthesia. OmniGuide Communications Inc. (OGCI) has fabricated a photonic bandgap fiber capable of flexibly guiding CO2 laser energy. Results of laryngeal in-vivo and in-vitro animal studies will be presented. We will discuss the system setup, fiber performance and clinical outcomes. In addition we will present the results of the first human treatment and highlight additional otolaryngology conditions, which will likely benefit from the new technology herein presented.

Heating of hollow photonic Bragg fibers from field propagation, coupling, and bending

We investigate heating from field propagation, coupling, and bending, which are the potential failure mechanisms for an emerging new type of high-power radiation guides-hollow photonic Bragg fibers. Continuous wave (CW) and pulsed radiation sources are considered, assuming continuous operation of the laser source.

Hollow-Core Fibers

This chapter discusses the properties, applications, and manufacture of hollow-core fibers. Hollow-core fibers guide light by means of a reflective cladding. Because the index of refraction of the hollow core is smaller than that of the cladding materials, the guiding mechanism cannot be based on total internal reflection, as is the case for traditional optical fibers. Instead, three major types of reflective cladding are used—a metal tube with optional dielectric coating, a multilayer dielectric Bragg mirror, or a two-dimensional photonic crystal. The simplest method for guiding light in a hollow core is by enclosing the core with a highly reflective metal. The metal acts as a mirror, so that fields from the core incident on the metal are reflected back into the core, providing the confinement mechanism. When the interior of the waveguide consists of a single homogeneous dielectric material, the mode fields can be separated into two polarizations—transverse electric and transverse magnetic with vanishing axial components of the electric and magnetic fields, respectively.