Computational analysis of a scalable optically homogeneous free-space interferometer.

This study describes a scalable optically homogeneous free-space interferometer. Computationally modeled as an unbroken block of fused silica, the interferometer's six-sided design is simple and intuitive, exploiting total internal reflection and refraction to split and recombine a collimated input beam. During propagation, one portion of the split beam remains within the substrate to act as a reference beam. The second portion of the split beam is exposed to the surrounding environment, enabling real-world environment characterization in real time. Validation of the interferometer concept is performed using numerical and analytical techniques. Based on its scalability and robustness, the proposed interferometer design is primed for applications in atmospheric sensing, passive chemical detection, and spaceborne technologies.

Capturing multiple full-scene images with a single camera via aperture stop exploitation.

In an effort to increase the capability of modern camera systems, recent advances in imaging technology have seen the maturation of postprocessing and demosaicing algorithms, multispectral imagers, and scene-splitting techniques. Although highly enabling, each of these methods faces an inherent limitation imposed by the camera's geometry. By reevaluating the fundamental components of the camera, this study presents a new method and paradigm in capturing and processing scene information. The proposed camera design is validated and optimized using Zemax simulations. The results show that light entering a camera can be split into three independent, spatially separated, full-scene images, wherein each image retains all spectral, polarimetric, and relative intensity information of the original scene.

Fabrication of metal-oxide nano-hairs for effective index optical elements.

We present a method for fabricating high aspect ratio metal-oxide, sub-wavelength grating structures. These "nano-hair" structures are composed of alumina cylindrical pillars, partially embedded in a supporting fused silica substrate. The fabricated nano-hair structures demonstrate phase control of the transmitted beam while maintaining a peak transmitted power greater than 93% around a central wavelength of λ(o) = 1.55 µm. Based on this principle, discrete and continuous phase functions can be encoded by controlling the lithographic process.

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.

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.

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.