Michael T. Gallagher

Low-loss hollow-core silica/air photonic bandgap fibre

Photonic bandgap structures use the principle of interference to reflect radiation. Reflection from photonic bandgap structures has been demonstrated in one, two and three dimensions and various applications have been proposed. Early work in hollow-core photonic bandgap fibre technology used a hexagonal structure surrounding the air core; this fibre was the first demonstration of light guided inside an air core of a photonic bandgap fibre. The potential benefits of guiding light in air derive from lower Rayleigh scattering, lower nonlinearity and lower transmission loss compared to conventional waveguides. In addition, these fibres offer a new platform for studying nonlinear optics in gases. Owing largely to challenges in fabrication, the early air-core fibres were only available in short lengths, and so systematic studies of loss were not possible. More recently, longer lengths of fibre have become available with reported losses of 1,000 dB km-1. We report here the fabrication and characterization of long lengths of low attenuation photonic bandgap fibre. Attenuation of less than 30 dB km-1 over a wide transmission window is observed with minimum loss of 13 dB km-1 at 1,500 nm, measured on 100 m of fibre. Coupling between surface and core modes of the structure is identified as an important contributor to transmission loss in hollow-core photonic bandgap fibres.

Soliton pulse compression in photonic band-gap fibers.

We report on pulse compression using a hollow-core photonic band-gap fiber filled with Xe. Output pulses with megawatt peak powers and durations of 50 fs have been generated from 120-fs input pulses. The large third-order dispersion inherent in these fibers degrades the optimal compression ratio and prevents generation of even shorter pulses. Nevertheless, for picosecond input pulses, compression to less than 100 fs is predicted.

Highly birefringent hollow-core photonic bandgap fiber

A highly birefringent hollow-core photonic bandgap fiber is fabricated and characterized. The fiber group birefringence is found to be 0.025 at 1550 nm through wavelength scanning method and direct measurement of differential group delay.

Silica-glass contribution to the effective nonlinearity of hollow-core photonic band-gap fibers

We measure the effective nonlinearity of various hollow-core photonic band-gap fibers. Our findings indicate that differences of tens of nanometers in the fiber structure result in significant changes to the power propagating in the silica glass and thus in the effective nonlinearity of the fiber. These results show that it is possible to engineer the nonlinear response of these fibers via small changes to the glass structure.

Photonic Crystal Fibers: Effective-Index and Band-Gap Guidance

Conventional telecommunication optical waveguide glass fiber is the backbone of the internet revolution. This highly optimized and highly transparent waveguide consists of a higher refractive index core glass inside a lower index clad glass. Light is localized in the core by total internal reflection (TIR) at the core/clad boundary. The transmission distance between amplifiers of today’s fibers, about 80–120 km, is limited in part by the small but nonzero absorption and scattering of the fiber. Longer transmission lengths could be possible by increasing the power at each amplifier, but this is limited by optical nonlinearity of the glass in the fiber.

Photonic crystal fibers

In recent years several new classes of fibers have emerged based on the same basic technological platform - air/silica microstructures. Though they are often referred to collectively these fibers can be divided into three very different classes: air-clad core fibers, effective-index fibers and photonic band-gap fibers. Although all act as waveguides, these groups of fibers exhibit different optical properties leading to different applications. We briefly discuss the air-clad core and effective index fibers before concentrating on the more unusual photonic band-gap fiber. With losses as low as 2.6 dB/km for effective index photonic crystal fibers (PCF) and 1 dB/m for band-gap fibers, this technology is beginning to show its potential for becoming a platform for more than just unique fiber-based components.

Surface modes and loss in air-core photonic bandgap fibers

We briefly review recent progress in the fabrication and characterization of air-core photonic band-gap fibers. These are silica fibers with an hexagonal array of air holes in the cladding, and a larger air hole creating the core. Improved structural uniformity transverse to the fiber axis and down the fiber axis has yielded fibers with better transmission characteristics. We have measured a minimum loss of 13 dB/km at 1500 nm for a 100 m length of our fiber. This is a marked improvement over previous loss measurements for air-core fibers of any kind. A comparison of observed spectra and calculated gap modes suggests that coupling between surface modes and core modes may be an important contributor to the remaining loss. We present a detailed analysis of the expected losses associated with mode crossings between the fundamental core mode and surface modes, showing that Lorentzian-shaped loss peaks are predicted.

Progress in high-power fiber lasers

We review current work on fiber laser systems at Corning. In particular, we describe design and performance of all-glass double-clad laser fibers, broad-area laser pumps, and pump coupling optics. We discuss our approaches using single-polarization fiber and low-nonlinearity photonic band gap fiber as technologies for developing the next generation of high-power fiber lasers.

Photonic band-gap fiber: fiber of the future?

We briefly review the state-of-the art in photonic band-gap fibers. Recent reduction in attenuation to 13 dB/km demonstrates the potential of these hollow-core fibers to provide low-loss and low-nonlinearity for a variety of applications including transmission fiber.

Generation of high-power, non-frequency shifted solitons in a gas-filled photonic band-gap fiber

We generate femtosecond, non-frequency shifted solitons with peak powers greater than 5 MW in a Xe-filled, hollow-core photonic band-gap fiber. This represents, to our knowledge, the first observation of temporal solitons with no self-frequency shift.