Single-mode tellurite glass holey fiber with extremely large mode area for infrared nonlinear applications.

We report the fabrication of a large mode area tellurite holey fiber from an extruded preform, with a mode area of 3000microm(2). Robust single-mode guidance at 1.55microm was confirmed by both optical measurement and numerical simulation. The propagation loss was measured as 2.9dB/m at 1.55microm. A broad and flat supercontinuum from 0.9 to 2.5microm with 6mW output was obtained with a 9cm length of this fiber.

The effect of periodicity on the defect modes of large mode area microstructured fibers.

It is well known that periodic variations in refractive index can be used to create guidance in an optical fiber via photonic bandgap effects. It has also been shown that periodic structure in index-guiding microstructured fibers can lead to the guidance of additional leaky higher-order modes due to bandgap effects. Here we demonstrate that this additional guidance mechanism can have important practical implications in large mode area silica microstructured fibers. We also demonstrate that similar modes can exist when a bandgap is not present and attribute this guidance to a low density of states. Excellent agreement between theoretical predictions and experimental observations is demonstrated. We explore the impact of these additional modes on the practical operation of these fibers and explore ways of minimizing their effects via the fiber geometry.

Square core jacketed air-clad fiber.

We report the fabrication of a highly multi-mode square core jacketed air-clad fiber with a top-hat near-field intensity profile. Using this fiber to deliver Q-switched pulses at 1 mum we have successfully produced square shaped ablation marks in indium tin oxide (ITO) without the use of complex beam shaping optics.

Microstructured fibers for broadband wavefront filtering in the mid-IR.

The European Space Agency's space-based Darwin mission aims to directly detect extrasolar Earth-like planets using nulling interferometry. However, in order to accomplish this using current optical technology, the interferometer input beams must be filtered to remove local wavefront errors. Although short lengths of single-mode fiber are ideal wavefront filters, Darwin's operating wavelength range of 4 - 20 microm presents real challenges for optical fiber technology. In addition to the fact that step-index fibers only offer acceptable coupling efficiency over about one octave of optical bandwidth, very few suitable materials are transparent within this wavelength range. Microstructured optical fibers offer two unique properties that hold great promise for this application; they can be made from a single-material and offer endlessly single-mode guidance. Here we explore the advantages of using a microstructured fiber as a broadband wavefront filter for 4 - 20 microm.