Andrew M. Kowalevicz

Photonic device fabrication in glass by use of nonlinear materials processing with a femtosecond laser oscillator.

Single-mode X couplers and three-dimensional waveguides are fabricated in transparent glasses by use of an unamplified femtosecond laser generating energies of up to 100 nJ. Changing fabrication parameters such as power and scanning speed permits creation of waveguides with a wide range of structures and refractive-index difference. Optical coherence tomography shows large refractive-index changes of up to ~10(-2) in the waveguides; these changes are consistent with guided mode analysis.

Three-dimensional photonic devices fabricated in glass by use of a femtosecond laser oscillator

Three-dimensional photonic waveguide devices are fabricated in glass by use of femtosecond pulses from an extended-cavity laser oscillator. Three-dimensional devices, including a symmetric three-waveguide directional coupler and a three-dimensional microring resonator, are fabricated and tested. Waveguides can be fabricated at depths of approximately 1 mm inside a glass substrate, thus demonstrating the capability of achieving dramatic increases in device density. These results demonstrate the potential to fabricate new classes of devices that are not possible in two dimensions.

Fabrication of coupled mode photonic devices in glass by nonlinear femtosecond laser materials processing

Coupled mode devices are fabricated in transparent glasses by nonlinear materials processing with femtosecond laser pulses. Using the direct output of an extended cavity femtosecond laser, without the need for a laser amplifier, single mode waveguides can be rapidly fabricated with well controlled parameters. A variety of photonic waveguide devices are demonstrated. Directional couplers with various interaction lengths and coupling coefficients are fabricated and their coupling properties are characterized. Measurements demonstrate coupled mode behavior consistent with theory. An unbalanced Mach-Zehnder interferometer is also fabricated and demonstrated as a spectral filter.

Ultrahigh resolution optical coherence tomography using a superluminescent light source

A superluminescent Ti:Al2O(3) crystal is demonstrated as a light source for ultrahigh resolution optical coherence tomography (OCT). Single spatial mode, fiber coupled output powers of ~40 microW can be generated with 138 nm bandwidth using a 5 W frequency doubled, diode pumped laser, pumping a thin Ti:Al2O(3) crystal. Ultrahigh resolution OCT imaging is demonstrated with 2.2 microm axial resolution in air, or 1.7 microm in tissue, with >86 dB sensitivity. This light source provides a simple and robust alternative to femtosecond lasers for ultrahigh resolution OCT imaging.

Generation of 150-nJ pulses from a multiple-pass cavity Kerr-lens modelocked Ti:Al2O3 oscillator

A high-pulse-energy, prismless, Kerr-lens mode-locked, extended cavity Ti:sapphire laser is demonstrated with double-chirped mirrors and a multiple-pass cavity. The laser operates at 5.85-MHz repetition rate and generates pulse energies as high as 150 nJ with 43-fs pulse duration, corresponding to peak powers of 3.5 MW directly from the laser.

Ultralow-threshold Kerr-lens mode-locked Ti:Al 2 O 3 laser

An ultralow-threshold Kerr-lens mode-locked Ti:Al(2)O(3) laser achieved by use of an extended cavity design is demonstrated. Mode-locking thresholds as low as 156 mW are achieved. Pulses with durations as short as 14 fs and bandwidths of >100 nm with output powers of ~15 mW at 50-MHz repetition rates are generated by only 200 mW of pump power. Reducing the pump power requirements to a factor of 10x less than required by most conventional Kerr-lens mode-locked lasers permits inexpensive, low-power pump lasers to be used. This will facilitate the development of low-cost, high-performance femtosecond Ti:Al(2)O(3) laser technology.

Compact femtosecond lasers based on novel multipass cavities

This paper provides a comprehensive description of the design of compact femtosecond solid-state lasers that are based on novel multipass cavity (MPC) configurations to extend the resonator length. Of special importance are the q-preserving MPCs, which leave invariant the original spotsize distribution and Kerr lens mode-locking point of the short cavity. The general design guidelines of q-preserving MPCs are first reviewed and a novel configuration is proposed for the case where the MPC consists of notch mirrors. A class of non-q-preserving compact cavities is also analyzed and conditions needed to minimize the deviation from the q-preserving configuration are discussed. The design and performance of a q-preserving and a non-q-preserving mode-locked Ti:Al/sub 2/O/sub 3/ laser are then described as examples. These compact oscillators measuring only 30 cm /spl times/ 45 cm could produce pulses as short as 19 fs at a repetition rate of around 31 MHz. Up to /spl sim/3.6 nJ of pulse energy could be obtained with only /spl sim/1.5 W of pump power. Finally, two-mirror MPC geometries are examined to investigate the limits of compactness and energy scaling.

An extended cavity femtosecond Cr:LiSAF laser pumped by low cost diode lasers.

We describe an extended cavity femtosecond Cr:LiSAF laser pumped by inexpensive single spatial mode diodes. Using a multi-pass cavity (MPC) to lower the repetition rate and a saturable Bragg reflector (SBR) for mode-locking, pulse energies of 0.75 nJ at a repetition rate of 8.6 MHz are achieved with durations of 39 fs and bandwidths of 20 nm in a prismless configuration. Pulse energies of 0.66 nJ at a repetition rate of 8.4 MHz with durations of 43 fs and bandwidths of 18.5 nm are generated using prisms for dispersion compensation. This laser offers performance approaching that of standard Ti:sapphire lasers at a fraction of the cost.

Photonic Device Fabrication With Femtosecond Laser Oscillators

With Femtosecond Laser Oscillators High-repetition-rate femtosecond laser oscillators are powerful tools for device fabrication. Today, waveguides can be written at speeds much higher than those that are possible using femtosecond amplifiers.

High-performance, compact, prismless, low-threshold 30-MHz Ti:Al2O3 laser

We describe the design and operation of a compact femtosecond Ti:Al2O3 laser based on a novel multipass cavity (MPC) design. The laser is all solid state, has prismless dispersion compensation with double-chirped mirrors, and uses a tight-focusing geometry to facilitate efficient low-threshold operation. We increase output pulse energies by extending the resonator length with a compact, scalable MPC, which preserves the characteristics of the Gaussian beam for the short cavity. Although the effective cavity length is approximately 5 m, an extremely compact laser that measures only 30 cm x 45 cm is achieved. With only 1.5 W of pump power, the laser generates 23-fs pulses at a repetition rate of 31.25 MHz and with 88 mW of average output power, corresponding to 2.8 nJ of pulse energy.