John E. McCarthy

Mid-infrared spectral broadening in an ultrafast laser inscribed gallium lanthanum sulphide waveguide

We report the successful fabrication of mid-infrared waveguides written in a gallium lanthanum sulphide (GLS) substrate via the ultrafast laser inscription technique. Single mode guiding at 2485 nm and 3850 nm is observed. Spectral broadening spanning 1500 nm (-15dB points) is demonstrated under 3850 nm excitation.

Experimental demonstration of spectral broadening in an all-silica Bragg fiber

We present the first report on experimental observation of nonlinear spectral broadening in an all-solid photonic band gap Bragg fiber of relatively large mode area approximately 62 microm(2). The theoretically designed Bragg fiber for this specific application was fabricated by the well known MCVD technique. Nonlinear spectral broadening was observed by launching high power femtosecond pulses of 1067 nm pump wavelength. These first results indicate that fabrication of such Bragg fibers, once perfected, should potentially serve as an alternative route for realization of supercontinuum light.

Spectrally tailored mid-infrared super-continuum generation in a buried waveguide spanning 1750 nm to 5000 nm for atmospheric transmission

We show how nonlinear spectral broadening in a buried chalcogenide mid-infrared waveguide can be used to reshape the spectrum of a femtosecond pulse train at 4260 nm in order to reduce the effects of atmospheric absorption due to carbon dioxide. The nonlinear spectral broadening results in the source with −20 dB spectral width spanning over 3500 nm, from 1700 nm to 5200 nm. This represents a potential route to tailored sources for long-range mid-infrared applications.

Two Octaves Supercontinuum Generation in Lead-Bismuth Glass Based Photonic Crystal Fiber

In this paper we report a two octave spanning supercontinuum generation in a bandwidth of 700–3000 nm in a single-mode photonic crystal fiber made of lead-bismuth-gallate glass. To our knowledge this is the broadest supercontinuum reported in heavy metal oxide glass based fibers. The fiber was fabricated using an in-house synthesized glass with optimized nonlinear, rheological and transmission properties in the range of 500–4800 nm. The photonic cladding consists of 8 rings of air holes. The fiber has a zero dispersion wavelength (ZDW) at 1460 nm. Its dispersion is determined mainly by the first ring of holes in the cladding with a relative hole size of 0.73. Relative hole size of the remaining seven rings is 0.54, which allows single mode performance of the fiber in the infrared range and reduces attenuation of the fundamental mode. The fiber is pumped into anomalous dispersion with 150 fs pulses at 1540 nm. Observed spectrum of 700–3000 nm was generated in 2 cm of fiber with pulse energy below 4 nJ. A flatness of 5 dB was observed in 950–2500 nm range.

Ultrafast laser inscription of mid-IR integrated optics for astronomy

The development of integrated optical (IO) circuits for mid-IR radiation (wavelengths from ∼3 to ∼30 µm) is of significant interest for applications in bio-sensing and astronomy [1]. With specific reference to astronomy, the mid-IR spectrum is of particular interest since this is the region where objects such as planets, at earth-like temperatures, can be probed. It is also the region where biomarkers such as H<inf>2</inf>O, CO<inf>2</inf> and O<inf>3</inf> can be identified.

Mid-infrared photonics enabled by 3D laser writing chalcogenide glass

Recent results from our work using ultrafast laser writing to fabricate waveguides and on-chip devices inside sulphide chalcogenide glasses are presented in this paper. Low loss single-mode (SM) and multi-mode (MM) waveguide arrays were successfully laser fabricated, for the first time to our knowledge, for operation in the whole near-IR (NIR) to mid- IR (MIR) range (1 to 11 μm wavelengths). These waveguides are demonstrated to have numerical apertures (NA) which can exceed NA=0.2, therefore also allowing for low bend losses as well as direct coupling to QC lasers. We also demonstrate the control over the waveguide mode field diameters (MFDs) (at 1/e2) by changing the waveguide core sizes and index contrasts, achieving typical values of 44 μm at 10.6 μm, down to 6 μm for telecom 1.55 μm light. The optical nonlinear properties of these waveguides have also been preliminarily investigated. Using a femtosecond (fs) optical parametric amplifier system, the optical nonlinearity of bulk gallium lanthanum sulphide (GLS) glass was first measured at 2.5 μm. The upper limits for the nonlinear properties of the laser modified material could be estimated based upon the nonlinear spectral broadening of a 2.5 μm fs pulse train coupled into SM waveguides. Further work includes the demonstration of on-chip three dimensional (3D) beam combiners for the MIR range (10.6 μm in this work), for near future implementation in astronomical observatories for stellar interferometry.

Mid-Infrared guiding and nonlinear spectral broadening in ultrafast laser inscribed gallium lanthanum sulphide waveguides

Spectral broadening spanning 850 nm (-15 dB points) was observed in an ultrafast laser inscribed gallium lanthanum sulphide waveguide under excitation of femto-second laser radiation with a central wavelength of 2.35 μm.