This Small Business Innovation Research (SBIR) Phase II project will develop a new type of optical power monitor utilizing transparent microwires and nanowires patterned within a multi-layer anti-reflection coating. These "wires" are nanometer to micron wide traces defined within a transparent indium tin oxide (ITO) conductive layer. ITO typically absorbs 1 to 10% at visible and infrared wavelengths, depending on its thickness, and optical intensities greater than 1 mW/mm2 produce measureable localized heating. This temperature change induces a proportional resistance change that can be measured electronically. By inserting this detector in-line between fiber optic cables, the optical power of the internal signals can be measured without degrading the signal strength. Moreover, by reducing the dimensions of the trace to the nanometer scale, the detector also has the potential for high-speed operation with a bandwidth approaching GHz.
The broader impact/commercial potential of this project includes new optical monitoring applications that were previously impossible or impractical. In one example, inexpensive and miniature optical monitors can now be integrated within the hundreds of millions of fiber optic interconnects produced annually for fiber optic communication systems. Advanced self-monitoring and self-diagnosing communication network architectures can be developed for Fiber-to-the-Home networks and data centers by transparently measuring the optical power through fiber optic junctions. This technology promises to reduce the cost to measure power within optical fibers by two orders of magnitude, and has the potential to be mass-produced and even inkjet printed on flexible plastic film, window glass, solar panels, mirrors, displays, or even on curved substrates such as light bulbs and lenses.
Indium tin oxide (ITO) is an optically transparent, conductive thin film coating that is typically deposited by sputtering on glass or plastic substrates and commonly found in touch screens and flat panel displays. In this project, ITO coatings have been used in a non-traditional way to measure optical power, by developing new microwire detector designs and advanced lithographic and packaging processes. The absorption of ITO is sufficiency high that the coating experiences a significant temperature rise upon illumination. The coating is lithographically patterned to form a detector comprised of resistive traces about 5 microns in width. By illuminating the trace by an optical beam, the optical power passing through can be determined based on its measured resistance change. This detector is "non-invasive" in the sense that nearly all optical power passes through the thin film detector. A wide range of transparent microwire detectors have been fabricated, including single channel and twelve channel fiber coupled optical monitors. Experiments have validated that this optical detector provides a precise measure of optical power without significantly attenuating the beam. The ability to coat and pattern this coating on any optical surface, curved or flat, glass or plastic, enables a simple, high performance and cost effective solution to provide optical power monitoring functionality in applications where it has previously been impractical. One particular application of this new technology is to measure optical power in the 100 million fiber optic connector adapters produced annually for fiber optic communication systems in data centers and telecom networks. These adapters are located on nearly all fiber optic routers, switches, transmitters, amplifiers, filters and patch-panels.
