Optical technology plays an increasingly important role in numerous information system applications, including optical communications, storage, signal processing, biology, medicine, and sensing. As optical technology develops, there is a growing need to develop scalable and reliable photonic integration technologies. These include the development of passive and active optical components that can be integrated into functional optical circuits and systems, including filters, electrically or optically controlled switching fabrics, optical sources, detectors, amplifiers, etc. We explore the unique capabilities and advantages of nanotechnology in developing next generation integrated photonic information systems. Our approach includes design, modeling and simulations of selected components and devices, their nanofabrication, followed by validation via characterization and testing of the fabricated devices. The latter exploits our recently constructed near field complex amplitude imaging tool. The understanding of near field interactions in nanophotonic devices and systems is a crucial step as these interactions provide a variety of functionalities useful for optical systems integration. Furthermore, near-field optical devices facilitate miniaturization, and simultaneously enhance multifunctionality, greatly increasing the functional complexity per unit volume of the photonic system. Since the optical properties of near-field materials are controlled by the geometry, there is flexibility in the choice of constituent materials, facilitating the implementation of a wide range of devices using compatible materials for ease of fabrication and integration.
A thin layer of SU-8 submicron pattern produced by holographic lithography is used as the dry etch mask in a chemically assisted ion beam etching (CAIBE) system. The effect of the chlorine gas flow rate on etched sidewalls is investigated; by matching the lateral etch rate and the deposition rate, etching selectivity of up to 7:1 is achieved, rendering smooth vertical sidewalls and damage-free upper portions for the etched structure.
We describe an approach to use the thin layer of SU-8 submicron pattern produced by holographic lithography as dry etching mask in chemically assisted ion beam etching (CAIBE) system. The effect of chlorine gas flow on etched sidewall was investigated; by matching the lateral etch and deposition rate, etching selectivity of about 7:1 has been achieved with vertical and smooth sidewall and damage-free upper portion of the etched structure. As an application, a half wavelength retardation plate for 1.55 mm wavelength was designed, fabricated and characterized.
Approaches to create radially and azimuthally polarized light beams usually suffer from issues of integration difficulty and system complexity. In this research, we apply a compact design of space-variant inhomogeneous media (SVIM), providing an even more compact solution with relatively higher conversion efficiency. The device we utilize to convert linear polarization at the wavelength of 10.6 μm to radial/azimuthal polarization is fabricated on a single GaAs substrate, using space-variant subwavelength periodic structure with locally varying form birefringence. Unlike previous approach, this subwavelength periodic structure is designed to be relatively deep in order to introduce a pi phase shift between the TE and the TM components of the input light, and therefore to locally rotate the incident linearly polarized light to the radial/azimuthal direction. To realize the deep space-variant form birefringent structure, we utilize standard photolithography on a GaAs substrate, followed by chemically assisted ion beam etching (CAIBE), rendering an etch profile with high aspect-ratio (6:1) as required by the original design. An optical characterization at 10.6 μm shows a close match between the measured and the theoretical polarization distribution. With proper control of the etch profile it shows that the subwavelength structure also serves as an anti-reflection coating at the sample surface.
Optical technology plays an increasingly important role in numerous applications areas, including communications, information processing, and data storage. However, as optical technology develops, it is evident that there is a growing need to develop reliable photonic integration technologies. This will include the development of passive as well as active optical components that can be integrated into functional optical circuits and systems, including filters, switching fabrics that can be controlled either electrically or optically, optical sources, detectors, amplifiers, etc. We explore the unique capabilities and advantages of nanotechnology in developing next generation integrated photonic chips. Our long-range goal is to develop a range of photonic nanostructures including artificially birefringent and resonant devices, photonic crystals, and photonic crystals with defects to tailor spectral filters, and nanostructures for spatial field localization to enhance optical nonlinearities, to facilitate on-chip system integration through compatible materials and fabrication processes. The design of artificial nanostructured materials, PCs and integrated photonic systems is one of the most challenging tasks as it not only involves the accurate solution of electromagnetic optics equations, but also the need to incorporate the material and quantum physics equations. Near-field interactions in artificial nanostructured materials provide a variety of functionalities useful for optical systems integration. Furthermore, near-field optical devices facilitate miniaturization, and simultaneously enhance multifunctionality, greatly increasing the functional complexity per unit volume of the photonic system. Finally and most importantly, nanophotonics may enable easier integration with other nanotechnologies: electronics, magnetics, mechanics, chemistry, and biology.
We describe a novel approach to manufacture photonic crystal-based integrated systems based on a two-step process of interferometric patterning followed by optical direct-write of the functional elements. First, the photonic crystal lattice is patterned in photoresist using interferometric lithography, producing a large-area lithographic pattern quickly and easily. Second, the defects in the lattice to implement the functional devices are created using optical direct write with a strongly focused optical beam. After patterning processes, the mask is developed and a dry-etching process is used to transfer the pattern into the substrate. This hybrid approach possesses an advantage in terms of fabrication time and cost as compared to E-beam lithography for the patterning of large-scale photonic crystal-based systems.
We discuss various practical points in the design, fabrication and characterization of form birefringent retardation plates in GaAs. The role of the substrate in the device performance is presented, together with the importance of using anti-reflection coatings. Also, we discuss the specific case of metallic reflection gratings in GaAs substrates and the resulting enhanced retardation. Finally we present the results of thermal tuning of a nominally half-wave subwavelength retardation plate.