Aaron J. Pung

Integrated Tm:fiber MOPA with polarized output and narrow linewidth with 100 W average power

We report on a Tm:fiber master oscillator power amplifier (MOPA) system producing 109 W CW output power, with >15 dB polarization extinction ratio, sub-nm spectral linewidth, and M2 <1.25. The system consists of polarization maintaining (PM) fiber and PM-fiber components including tapered fiber bundle pump combiners, a single-mode to large mode area mode field adapter, and a fiber-coupled isolator. The laser components ultimately determine the system architecture and the limits of laser performance, particularly considering the immature and rapidly developing state of fiber components in the 2 μm wavelength regime.

Blue Laser Diode Wavelength Selection With a Variable Reflectivity Resonant Mirror

A guided-mode resonance filter is designed and fabricated for externally locking a GaN blue laser diode. The external mirror design is polarization selective which allows the reflectivity to be tuned, in order to optimize the output coupling of the cavity. The resonance demonstrates a line-width <;0.5 nm, centered at 445.6 nm with an output power in excess of 0.5 W of CW power without temperature control.

Correlation of Fabrication Tolerances with the performance of Guided-Mode-Resonance Micro-optical components

Large-scale fabrication of micro-optical Guided-Mode-Resonance (GMR) components using VLSI techniques is desirable, due to the planar system integration capabilities it enables, especially with laser resonator technology. However, GMR performance is dependent on within-wafer as well as wafer-to-wafer lithographic process variability, and pattern transfer fidelity of the final component in the substrate. The fabrication of lithographs below the g-line stepper resolution limit is addressed using multiple patterning. We report results from computational simulations, fabrication and optical reflectance measurements of GMR mirrors and filters (designed to perform around the wavelength of 1550nm), with correlations to lithographic parameter variability, such as photoresist exposure range and etch depth. The dependence of the GMR resonance peak wavelength, peak bandwidth are analyzed as a function of photolithographic fabrication tolerances and process window.

Spatial multiplexing for blue lasers for undersea communications

Space division multiplexing of optical beams has recently been demonstrated for improving the bandwidth of optical communication links. This paper will explore the use of space division multiplexing utilizing blue lasers for potential undersea applications. Experimental results will be shown for optical vortices utilizing a range of charge numbers corresponding to various Orbital Angular Momentum states.

Method of Fabrication for Encapsulated Polarizing Resonant Gratings

In this letter, we present a novel method of fabricating encapsulated resonant gratings. The fabrication method uses selective etching, conformal deposition, conventional lithography, and direct bonding techniques. Our letter includes simulation and experimental results, confirming a strong resonance unique to the TE polarization at 1550 nm with a 5 nm full-width at half-maximum.

Two-dimensional guided mode resonance filters fabricated in a uniform low-index material system

We demonstrate the fabrication, simulation, and experimental results of a buried, homogeneous narrowband spectral filter with a periodic, hexagonal unit cell of air pockets, encapsulated in a fused silica substrate. The leaky waveguide is formed by depositing SiO(x) on an etched fused silica grating via plasma-enhanced chemical vapor deposition. Design principles of guided mode resonance filters were utilized to achieve a resonance with 60% reflectivity at a wavelength of 1.741 μm. The device demonstrates resonance with FWHM of 6 nm.

Polarization selective, graded-reflectivity resonance filter, using a space-varying guided-mode resonance structure.

We designed, fabricated, and tested, polarization selective, graded-reflectivity resonant filters; based on a radial-gradient spatially-distributed, guided-mode resonance device architecture. The demonstrated filters have polarized spectral-resonance responses, distributed across their aperture extent, in the range between 1535 nm and 1540 nm wavelengths. Spectral sensitivity was observed on device tests, for wavelength changes as low as 0.2 nm. Using multiple lithographic exposures and biasing exposure methods, the devices were engineered to have a sub-aperture region, with no hard boundaries or diffraction anomalies.

Wavelength Selection and Polarization Multiplexing of Blue Laser Diodes

An external laser cavity was constructed that utilizes polarization multiplexing to combine the emission from two gallium nitride blue laser diodes. A polarization-dependent narrow-band resonant mirror was designed to be the output coupler of this cavity, which locked both laser diodes at a fixed wavelength of 445.5 nm with a line-width of <;0.5 nm. Output powers from this system approached 0.7 W while maintaining complete spectral control.

Guided-Mode Resonance Filters for Wavelength Selection in Mid-Infrared Fiber Lasers

A narrowband mid-infrared (mid-IR) guided-mode resonance filter (GMRF) is designed and fabricated using a Hafnium Dioxide film/quartz wafer material system. The fabricated GMRF is then integrated into an erbium (Er)-doped Zr-Ba-La-Al-Na (ZBLAN) fluoride glass fiber laser as a wavelength selective feedback element. The laser operated at 2782 nm with a line-width less than 2 nm demonstrates the viability of GMRFs for wavelength selection in the mid-IR.

Continuous-wave laser damage of uniform and nanolaminate hafnia and titania optical coatings

The laser-damage thresholds of single material and nanolaminate thin films were compared under continuous-wave (CW) illumination conditions. Nanolaminate films consist of uniform material interrupted by the periodic insertion of one or more atomic layers of an alternative material. Hafnia and titania were used as the base materials, and the films were deposited using atomic-layer deposition. The nanolaminates were less polycrystalline than the uniform films, as quantified using x-ray diffraction. It was found that the nanolaminate films had reduced laser-damage thresholds on smooth and patterned substrates as compared to uniform single-material films. This behavior is unusual as prior art indicates that amorphous (less polycrystalline) materials have higher laser-damage thresholds under short-pulse excitation. It is speculated that this may indicate that local thermal conduction affects breakdown more strongly under CW excitation than the dielectric properties that are important for short-pulse excitation.