Guided-Wave Optics: the transmission of light through dielectric conduits was developed to provide long-distance light transmission wihout the use of relay lenses. The foundation of guided-wave optics come from John Tyndall's demonstration of total internal reflection in the 1800s. Since then, the technique of optical guiding has been developed and applied to direct light to akward places, establish secure communications and consruct miniaturized optical and optoelectronic devices requiring the confinement of light. The principle of optical confinement relies on the properties of a medium of one refractive index imbedded in another medium of lower refractive index: the optical trapping effect results from light rays that are confined by multiple total internal reflections. These light conduits transport light from one location to another with minimal intensity losses. An optical waveguide is a light conduit consisting of a slab, strip or cylinder of dielectric (non-conducting) material surrounded by another dielectric material of lower refractive index. The most widely used of these waveguides is the optical fiber, which is made of two concentric cylinders of low-loss dielectric material such as glass.

Intergrated optics is the technology of integrating various optical devices and components for the generation, focusing, splitting, combining, isolation, polarization, coupling, switching, modulation and the detection of light, all on a single substrate (chip). Optical waveguides provide the connections between these components. Such components are optical versions of electronic integrated circuits. Integrated optics has the potential to miniaturize optics, analoguous to how integrated circuits have miniaturized electronics.

Wave-Guide Geometry: include the strip, embedded-strip, the rib or ridge, and the strip-loaded. S bends are used to offset the porpagation axis. The Y branch plays the role of a beamsplitter or a combiner. Two Y branches may be used to make a Mach-Zehnder interferometer. Two waveguides in close proximity (or intersecting) can exchange power and may be used as directional couplers. The most advanced technology for fabricating wavelengths is Ti:NbO3. An ambedded-strip waveguide is fabricated by diffuing titanium into a lithium niobate substrate to raise its refractive index in the region of the strip. GaAs waveguides are made by using layers of GaAs and AlGaAs of lower refractive index. Glass waveguides are made by ion exchange (used to make light modulators and switches).

Research Proposal: Earlier advances towards optical circuity occurred in 2001 when Fortmann et al. discovered unexpected variances of optical properties in amorphous silicon upon infusion with hydrogen. The theoretical operations have been performed and the next setp is to send a laser through a sequence of optical elements and analyze the resultant beam. In an attempt to construct a light operated switch, we must demonstrate that a hydrogen infused amorphous silicon waveguide can transmit electromagnetic radiation efficiently; this is done by sending a collimated, micron width laser beam through the prepared silicon slab. At present, the major challenge is to correct the laser beam diameter and align the waveguide.

Abstract: An Experimental Evaluation of a Prototype Hydrogenated Amorphous Silicon Wave-Guide

Yiyi Deng, Ward Melville High School, East Setauket, NY; John Noé and Harold Metcalf, Laser Teaching Center, Dept. of Physics and Astronomy; Charles M. Fortmann, Dept. of Applied Math and Statistics, Stony Brook University.

Guided-Wave Optics involves the transmission of light through dielectric conduits and was originally developed to provide long-distance light transmission without the use of relay lenses. The principle of optical confinement relies on the properties of a medium of one refractive index (which could be in the form of a slab, strip or cylinder) embedded in another medium of lower refractive index; the optical trapping effect results from light rays that are confined by multiple total internal reflections. These light conduits transport light from one location to another with minimal intensity losses.

Fiber optics is the epitome of guided-wave optics at present, but future applications in integrated optical circuitry may prove even more significant in coming decades. Integrated optics is the technology of uniting various optical devices and components for the generation, focusing, splitting, combining, isolation, polarization, coupling, switching, modulation and the detection of light, all on a single substrate. Optical wave guides provide the connections between these components. Such components are optical versions of electronic integrated circuits. Integrated optics has the potential to miniaturize optics, analogous to how integrated circuits have miniaturized electronics.

In 2001, Fortmann et al. demonstrated that the refractive index of amorphous silicon can be dramatically altered upon infusion with hydrogen. The theoretical operations have been performed and a prototype device has been constructed. The prototype has a waveguide channel approximately 5 microns high, 30 microns wide, and 20 mm long. Our immediate goal is to demonstrate that this protototype hydrogen-infused amorphous silicon wave-guide can transmit electromagnetic radiation efficiently. This will be done by focussing laser light from a 1550 nm fiber-coupled laser into the channel at one end and detecting emerging light on the other side. The particular choice of 1550 nm is largely due this wavelength's reputation as a "communications wavelength," facilitating the application of the results in current optical integration technology. The major challenges of the experiment are properly shaping the laser beam at the fiber/wave-guide interface and correctly aligning the wave-guide in the x, y and z planes. At present, we are in the process of selecting suitable laser and motion translation components for purchase.

This research was supported by the Simons Foundation.

Components of Alignment Setup

Laser Shopping:

Germanium Detector Shopping:

Why the laser? All lasers (Light Amplification by Stimulated Emission of Radiation) produce intense beams of light that are monochromatic, coherent, and highly collimated. The wavelength (color) of the laser light is extremely pure (monochromatic) when compared to other sources of light, and all of the photons (energy) that make up the laser beam have a fixed phase relationship (coherence) with respect to one another. This causes the light to form a beam with a very low rate of expansion (low divergence) that can travel over great distances, or can be focused to a very small spot with a bright- ness that can approximate that of the sun. Because of these properties, lasers are used in a wide variety of applications. All lasers include a gain medium (the source of the laser light, e.g., argon gas), an excitation source (e.g., a power supply), and a resonator structure (mirrors or reflective surfaces aligned to reflect some or all of the emitted light back through the gain medium). Beyond these basic similarities, the lasers are all very different in their size, output, beam quality, power consumption, and operating life. There are three kinds of commercial lasers: gas lasers (helium neon, helium cadmium, and ion lasers), diode-pumped solid-state (DPSS) lasers, and semiconductor diode laser assemblies. Helium neon (HeNe) lasers are low in cost and have unsurpassed beam quality, but have relatively low output power (up to 30 nm. Air-cooled ion lasers produce output at a wide variety of wavelengths throughout the visible spectral region. DPSS lasers combine the low power consumption of the HeNe with the high output power of an ion laser. Semiconductor diode lasers operate in the red and near-infrared spectral regions with output power up to 10 mW and are quite small, use very little power and have very long operating lives. The particular choice of 1310 nm (or 1550) is largely due to its reputation as a "communications wavelength" that will be easier to present to integration technology in the future.

The Waveguide: dimensions are ~ 35microns by 2 microns (1 x 10^-4 cm) and 1.5 cm long; rectangular in cross section (not ideal, but we used a template that was designed to make contacts for solar cells)

Funding: Solar Physics Inc, Locust Valley, NY; US Naval Research Laboratory, National Renewable Energy Laboratory; NY State Sensor Center for Excellence; The SImons Foundation

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