Crossed-cell-tile multiplexed 1st-order gratings, for three-dimensional beam-splitter applications.

Oblique angle of incidence two-way and three-way beam splitters were designed and fabricated. The devices feature two first-order diffraction gratings, arrayed crossed in alternating adjacent tiles, resulting in conical diffraction spot separation of two 1-orders in orthogonal planes while overlapping the 0-order. The two-way beam splitter was designed for 0-order suppression.

Towards Two-Photon Polymerization-Compatible Diffractive Optics for Micro-Mechanical Applications.

Diffractive optics are structured optical surfaces that manipulate light based on the principles of interference and diffraction. By carefully designing the diffractive optical elements, the amplitude, phase, direction, and polarization of the transmitted and reflected light can be controlled. It is well-known that the propagation of light through diffractive optics is sensitive to changes in their structural parameters.

Numerical study of feature-distribution effects for anti-reflection structured surfaces on binary gratings.

Suppressing Fresnel reflections from dielectric boundaries using periodic and random antireflection structured surfaces (ARSSs) has been vigorously studied as an alternative to thin film coatings for high-power laser applications. A starting point in the design of ARSS profiles is effective medium theory (EMT), approximating the ARSS layer with a thin film of a specific effective permittivity, which has features with subwavelength transverse-scale dimensions, independent of their relative mutual positions or distributions. Using rigorous coupled-wave analysis, we studied the effects of various pseudo-random deterministic transverse feature distributions of ARSS on diffractive surfaces, analyzing the combined performance of the quarter-wave height nanoscale features, superimposed on a binary 50% duty cycle grating.

Discrimination Between Explosive Materials and Isomers Using a Human Color Vision-Inspired Sensing Method.

This paper describes the application of a human color vision approach to infrared (IR) chemical sensing for the discrimination between multiple explosive materials deposited on aluminum substrates. This methodology classifies chemicals using the unique response of the chemical vibrational absorption bands to three broadband overlapping IR optical filters. For this effort, Fourier transform infrared (FT-IR) spectroscopy is first used to computationally examine the ability of the human color vision sensing approach to discriminate between three similar explosive materials, 1,3,5,-Trinitro-1,3,5-triazinane (RDX), 2,2-Bis[(nitrooxy)methyl]propane-1,3,-diyldinitrate (PETN), and 1,3,5,7-Tetranitro-1,3,5,7-tetrazocane (HMX).

Analytical procedure to assess the performance characteristics of a non-spectroscopic infrared optical sensor for discrimination of chemical vapors.

An optical-filter-based sensor that was designed to mimic human color vision was recently developed. This sensor uses three mid-infrared optical filters to discriminate between chemicals with similar, strongly overlapping mid-infrared absorption bands. This non-spectroscopic technique requires no spectral scanning.

Diffraction efficiency performance of random anti-reflecting subwavelength surface structures on prefabricated fused silica binary gratings.

Random anti-reflecting subwavelength surface structures have been reported to enhance transmission of optical windows and lenses. Specifically, for fused silica substrates, 99.9% specular transmission has been verified by various groups.

Biomimetic Optical-Filter Detection System for Discrimination of Infrared Chemical Signatures.

Optical-filter-based chemical sensors have the potential to dramatically alter the field of hazardous materials sensing. Such devices could be constructed using inexpensive components, in a small and lightweight package, for sensing hazardous chemicals in defense, industrial, and environmental applications. Filter-based sensors can be designed to mimic human color vision.

Optical filter selection for high confidence discrimination of strongly overlapping infrared chemical spectra.

Optical filter-based chemical sensing techniques provide a new avenue to develop low-cost infrared sensors. These methods utilize multiple infrared optical filters to selectively measure different response functions for various chemicals, dependent on each chemical's infrared absorption. Rather than identifying distinct spectral features, which can then be used to determine the identity of a target chemical, optical filter-based approaches rely on measuring differences in the ensemble response between a given filter set and specific chemicals of interest.

Comparative discrimination spectral detection method for the identification of vapors using overlapping broad spectral filters.

We present a comparative discrimination spectral detection approach for the identification of chemical vapors using broad spectral filters. We applied the method to flowing vapors of as-received and non-interacting mixtures for the detection of the volatile components of a target chemical in the presence of interferents. The method is based on measurements of the overall spectral signature of the vapors, where the interferent spectrum largely overlaps the target spectrum.

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.

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.

Performance of conformal guided mode resonance filters.

Guided mode resonance (GMR) filters are highly functional micro-optics capable of narrowband spectral filtering. GMR devices have previously been demonstrated on flat substrates using a wide range of materials and configurations. In this Letter, we apply a soft lithographic technique followed by the deposition of dielectric layers to generate GMR filters on a concave lens surface.

Spectral narrowing and stabilization of thulium fiber lasers using guided-mode resonance filters.

We used guided-mode resonance filters (GMRFs), fabricated using thin-film deposition and chemical etching, as intracavity feedback elements to stabilize and narrow the output spectrum in thulium-doped fiber oscillators operating in the 2 μm wavelength regime, producing linewidths of <700 pm up to 10 W power levels. A Tm fiber-based amplified spontaneous emission source was used to characterize the reflective properties of the GMRFs. Linewidths of 500 pm and a 7.

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.

Spatial and spectral beam shaping with space-variant guided mode resonance filters.

Novel all-dielectric beam shaping elements were developed based on guided mode resonance (GMR) filters. This was achieved by spatially varying the duty cycle of a hexagonal-cell GMR filter, to locally detune from the resonant condition, which resulted in modified wavelength dependent reflection and transmission profiles, across the device aperture. This paper presents the design, fabrication, and characterization of the device and compares simulations to experimental results.