Ori Weisberg

Low-loss asymptotically single-mode propagation in large-core OmniGuide fibers

We present the light-propagation characteristics of OmniGuide fibers, which guide light by concentric multi-layer dielectric mirrors having the property of omnidirectional reflection. We show how the lowest-loss TE_01 mode can propagate in a single-mode fashion through even large-core fibers, with other modes eliminated asymptotically by their higher losses and poor coupling, analogous to hollow metallic microwave waveguides. Dispersion, radiation leakage, material absorption, nonlinearities, bending, acircularity, and interface roughness are considered with the help of leaky modes and perturbation theory, and both numerical results and general scaling relations are presented. We show that cladding properties such as absorption and nonlinearity are suppressed by many orders of magnitude due to the strong confinement in a hollow core, and other imperfections are tolerable, promising that the properties of silica fibers may be surpassed even when nominally poor materials are employed.

Use of the photonic band gap fiber assembly CO2 laser system in head and neck surgical oncology

Since its introduction by Jako and Strong in 1972, the benefit of the CO2 laser systems to the head and neck surgeon has been well established in the management of early glottic, supraglottic, oral and oropharyngeal, and hypopharyngeal squamous cell carcinoma. Advantages of the CO2 laser include accuracy, predictability, and limited transmission of energy to adjacent tissues. The beam traditionally has been directed by a micromanipulator affixed to a surgical microscope coupled with a HeNe “guidebeam” to allow the surgeon to appreciate the point of laser contact. Obviously, the CO2 laser is perhaps most limited by the requirement of exposure of the site requiring laser incision. Given the transoral approach to CO2 laser procedures in head and neck surgical oncology, patients with difficult laryngeal exposure as a result of factors such as a short or stiff neck, macroglossia, retrognathia, obesity, or cervical spine immobility can severely limit the use of traditional CO2 laser systems. Traditionally, the Nd:YAG laser has maintained its use in head and neck surgery because of the capability for a flexible fiber system. However, the Nd:YAG laser is significantly more expensive than the CO2 laser and results in less control of energy dispersion to adjacent tissues. OmniGuide, Inc. (Cambridge, MA) has developed a CO2 laser system based on a flexible fiber system to deliver CO2 laser energy. This photonic band gap fiber assembly (PBFA) allows for the direct delivery of CO2 energy to regions of the head and neck in which the direct visualization required for traditional CO2 laser systems cannot be acquired. The OmniGuide Fiber is a hollow-core fiber with a dielectric mirror lining. The mirror, composed of alternating layers of high and low refractive index materials, guides the light through the fiber by reflecting it back into the hollow core. The mirror is surrounded by outer cladding that serves merely as a mechanical support to the mirror. An additional braid-reinforced polyimide jacket provides the final mechanical protection to the fiber device. The distal end of the fiber is fitted with a metal sleeve that protrudes 3 mm beyond the end face of the fiber to protect the fiber end face from tissue debris. Helium is flown through the hollow core of the fiber to allow further protection of the fiber distal tip from tissue debris, cooling of the fiber, cooling of targeted tissue, and clearing of smoke and blood from the field of sight. A gas accessory unit regulates the flow of gas into the fiber such that flow is tied to laser use. Rates of approximately 2 L/minute when the laser is idle and 8 L/minute when laser is fired were used. A Luxar LX-20SP NovaPulse (Lumenis, Yokneam, Israel) is retrofitted with an OmniGuide adapter to allow attachment of the fiber through a standard ST connector to the laser. The OmniGuide adapter couples both the laser radiation and helium flow into the fiber (Fig. 1). Fiber outer diameter of 1.8 mm allows insertion through a variety of standard malleable handpieces (Steiner hand-piece; Karl Storz, Germany; Suction Coagulator, Tyco Health Care Group, Boulder, CO), and length of 1.5 m provides maximum maneuvering ability to the surgeon. The fiber and handpiece were used transorally through a rigid endoscope. The laser was used in both superpulsed and continuous modes. Output powers ranged from 2 W for superficial tissue ablation to 8 W for precise tissue incision. We present three cases illustrating various applications of the OmniGuide flexible fiber CO2 laser system in the management of the patient with head and neck cancer. These cases include examples of diagnostic dilemma From the Department of Head and Neck Surgery (F.C.H., R.S.W.), The University of Texas M.D. Anderson Cancer Center, Houston, Texas, U.S.A.; The Bobby R. Alford Department of Otolaryngology–Head and Neck Surgery (C.N.P.), Baylor College of Medicine, Houston, Texas, U.S.A.; OmniGuide, Inc. (G.S., O.W., D.S.T., C.A., E.H.), Cambridge, Massachusetts, U.S.A.; and the Massachusetts Institute of Technology (Y.F.), Cambridge, Massachusetts, U.S.A. Editor’s Note: This Manuscript was accepted for publication February 21, 2006. Send Correspondence to F. Christopher Holsinger, MD, FACS, Department of Head and Neck Surgery, The University of Texas M.D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030-4009, U.S.A. E-mail: holsinger@mdanderson.org.

Photonic bandgap fibers exploiting omnidirectional reflectivity enable flexible delivery of infrared lasers for tissue cutting

Laser cutting of human bone and tissue is one of the oldest and most widespread applications of biophotonics. Due to the unique absorption of different kinds of tissue, choosing an appropriate laser wavelength allows selective ablation of tissue. Consequently, a large variety of laser sources with different emission wavelengths have been successfully applied to an equally large variety of medical indications. However, only a limited set of successful tissue-interaction experiments have translated into standard minimally-invasive procedures. One of the main reasons for this discrepancy between medical research and clinical practice is the lack of a commercially viable, flexible, and easy-to-use fiber optic beam delivery systems for wavelengths longer than 2 μm. In this paper, we will show how OmniGuide fibers, a new type of photonic bandgap fibers, could solve this problem. Recent performance data will be presented for both straight and bent fibers, including losses and power capacity, for delivery of CO2 lasers. We will also highlight medical procedures where these fibers could find first applications.

Quantitative characterization of higher-order mode converters in weakly multimoded fibers

We present a rigorous analysis methodology of fundamental to higher order mode converters in step index few mode optical fibers. We demonstrate experimental conversion from a fundamental LP01 mode to the higher order LP11 mode utilizing a multiple mechanical bend mode converter. We perform a quantitative analysis of the measured light intensity, and demonstrate a modal decomposition algorithm to characterize the modal content excited in the fiber. Theoretical modelling of the current mode converter is then performed and compared with experimental findings.

Analysis of general geometric scaling perturbations in a transmitting waveguide: fundamental connection between polarization-mode dispersion and group-velocity dispersion

We develop a novel perturbation theory formulation to evaluate polarization-mode dispersion (PMD) for a general class of scaling perturbations of a waveguide profile based on generalized Hermitian Hamiltonian formulation of Maxwell’s equations. Such perturbations include elipticity and uniform scaling of a fiber cross section, as well as changes in the horizontal or vertical sizes of a planar waveguide. Our theory is valid even for discontinuous high-index contrast variations of the refractive index across a waveguide cross section. We establish that, if at some frequencies a particular mode behaves like pure TE or TM polarized mode (polarization is judged by the relative amounts of the electric and magnetic longitudinal energies in the waveguide cross section), then at such frequencies for fibers under elliptical deformation its PMD as defined by an intermode dispersion parameter t becomes proportional to group-velocity dispersion D such that t 5 lduDu, where d is a measure of the fiber elipticity and l is a wavelength of operation. As an example, we investigate a relation between PMD and group-velocity dispersion of a multiple-core step-index fiber as a function of the core‐clad index contrast. We establish that in this case the positions of the maximum PMD and maximum absolute value of group-velocity dispersion are strongly correlated, with the ratio of PMD to group-velocity dispersion being proportional to the core‐clad dielectric contrast.

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.

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.

Group-velocity dispersion and deterministic PMD of modes in a hollow omnidirectional Bragg fiber

This articles demonstrates and discusses the group velocity dispersion and deterministic polarization mode dispersion in an omnidirectional photonic bandgap Bragg fiber (OPBF). Analysis of the modes dispersion properties were obtained by a transfer matrix technique while PMD of the elliptically distorted OBPFs was calculated by using a Hamiltoninan formulation of Maxwells equation in terms of transverse components of electromagnetic fields.

Power capacity of hollow Bragg fibers, CW and pulsed CW sources

The power capacity and failure mechanisms for an emerging type of high power radiation guides - hollow photonic Bragg fibers (PBF) are investigated. CW and pulsed radiation are considered in the study assuming continuous operation of the laser source.

OmniGuide fibers: An enabling technology for materials processing using high power lasers

Laser marking, high-power laser cutting or medical applications such as endoscopy often require a laser beam to be delivered to a region separated from the location of the source. To achieve this, one can either use expensive, cumbersome articulated-arm/gantry solutions, or, potentially more flexible and cost-effective fiber solutions. At the 10.6 µm wavelength, where CO2 lasers are the lowest-cost, highest-power sources, there are no reliable fiber solutions available. Therefore articulated arms are often used despite their shortcomings. Alternatively, a wavelength where fibers are available is chosen, even if the lasers are far more expensive (e.g. Nd:YAG).Laser marking, high-power laser cutting or medical applications such as endoscopy often require a laser beam to be delivered to a region separated from the location of the source. To achieve this, one can either use expensive, cumbersome articulated-arm/gantry solutions, or, potentially more flexible and cost-effective fiber solutions. At the 10.6 µm wavelength, where CO2 lasers are the lowest-cost, highest-power sources, there are no reliable fiber solutions available. Therefore articulated arms are often used despite their shortcomings. Alternatively, a wavelength where fibers are available is chosen, even if the lasers are far more expensive (e.g. Nd:YAG).