Brian K. Thomas

Extending Effective Area of Fundamental Mode in Optical Fibers

High power fiber lasers have become well established in many commercial realms. However, the amplification of ultrafast pulses to higher pulse energies in ytterbium-doped fibers remains very challenging due to nonlinear effects. We have demonstrated a new class of optical fibers based on resonantly enhanced leakage channels to extend the effective mode area of conventional single mode fibers by over two orders of magnitudes. This new class of fibers paves the way for a new breed of diffraction-limited kW-level ultrafast lasers, which can usher in a new age of high peak and average power ultrafast laser science as well as many new industrial applications in material processing.

Fully Stabilized GHz Yb-Fiber Laser Frequency Comb

We demonstrate a fully stabilized GHz-spaced Yb-fiber laser frequency comb using a Yb-fiber femtosecond oscillator with 1.04 GHz fundamental repetition rate.

Self-referenced f CEO stabilization of a low noise femtosecond fiber oscillator

We spectrally broaden a low phase noise Yb-femtosecond similariton fiber oscillator to more than an octave bandwidth. Using the f-2f self-referencing scheme we detect and stabilize its carrier envelope offset frequency.

GHz Yb-femtosecond-fiber laser frequency comb

We demonstrate a Fabry-Perot cavity, passively saturable-absorber-modelocked Yb-fiber femtosecond oscillator with up to 1.04 GHz fundamental repetition rate, enabling octave spanning continuum generation and self-referenced fCEO stabilization.

Large effective mode area optical fibers for high-power lasers

Leakage channel fibers have demonstrated their ability to significantly extend the effective mode area of a fundamental mode while maintaining robust single mode operation. These fibers are designed to have strong built-in mode filtering which effectively suppresses the propagation of all higher order modes while keeping fundamental mode loss to a minimum, and, therefore, effectively extending the regime of single mode operation. Recently all-glass leakage channel fibers have been demonstrated as a significant improvement over designs with air holes. These all glass leakage channel fibers not only can be manufactured with much improved consistence and uniformity. They can also be handled and used as conventional fibers. More importantly, mode distortions from collapse of air holes in photonic crystal fibers during splicing and other end face treatments are largely eliminated. We will review some of the recent progress in this area.

Small core ultra high numerical aperture fibers with very high nonlinearity

We have demonstrated ultra high NA fibers of core diameters down to 1.2 mum, low confinement loss and very high nonlinearity. Efficient supercontinuum generation is demonstrated in a 2 mum core fiber. These fibers can also be spliced to conventional fibers with low loss.

Rapidly scanning Fourier transform spectrometer based on a GHz repetition rate Yb-fiber laser pair

We demonstrate a rapidly scanning all-fiber Fourier transform spectrometer based on a temporal scanning all-optical delay line constructed with two mode-locked 1-GHz Yb fiber lasers. An effective mirror scan rate of 7.5 km/s is achieved.

GHz Yb-Fiber Laser Frequency Comb for Spectroscopy Applications

We demonstrate a fully stabilized GHz-spaced Yb-fiber laser frequency comb using a Yb-fiber femtosecond oscillator with 1.04 GHz fundamental repetition rate designed for comb spectroscopy applications.

Coherent transfer over 1.1 spectral octave with a fiber frequency comb

Highly coherent optical frequency combs have applications ranging from broadband spectroscopy with high sensitivity and accuracy [1], to the spectral dissemination of optical frequency references [2], where coherently linking the visible spectrum to the telecom band is important for the development of novel ultra-stable lasers in the 1.5 µm spectral region as well as long-haul optical carrier transfer [3]. In this contribution, we report on coherent transfer over more than one spectral octave with a Yb-fiber frequency comb. This represents the largest spectral gap directly spanned between two ultra-stable lasers by a frequency comb to date.

Advanced specialty fiber designs for fiber lasers

Progress in advanced specialty fibers is the foundation to further breakthroughs in fiber lasers. Recently, we have been working to advance several areas of developments in specialty fibers and would like to review these efforts here. The first topic is in the further development of all-glass large core leakage channel fibers (LCF) for robust and practical solutions for power scaling. The second area is the development of wide band air-core fibers with an innovative square lattice cladding and the demonstration of a factor of two improvements in bandgap over conventional hexagonal lattice. These air-core fibers are critical for fiber delivery solution of both CW and pulsed fiber lasers in the future. The last topic is a new development in design and simulation of SBS gains in optical fibers by incorporating leaky acoustic modes. These leaky acoustic modes have been mostly overlooked so far. It is essential that they are considered in SBS simulations in fibers, because they are normal solutions to the acoustic waveguide equations and have similar loss to guided acoustic modes where the acoustic mode loss is dominated by material loss. This leads to much improved resolution of SBS gain spectrum in fibers and to new design insights to the limit of SBS suppression based on anti-guide acoustic waveguide designs.