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Method of Fabricating Low-Loss and Low-Noise Hollow Waveguides for Visible Wavelength Applications

Date Posted
U.S. Patent Pending


The invention is method of fabricating a hollow glass waveguide (tube that transmits light) that exhibits low loss in the visible or short-wave spectral region and is optimized for Raman spectroscopy or visible laser beam delivery. Prior art hollow capillaries suffer high optical loss and poor visible transmission, but the NETL invention produces these high-quality capillaries via a specialized deposition system. This technology is available for licensing and/or further collaborative research from the U.S. Department of Energy’s National Energy Technology Laboratory.

Currently, there are no high-quality commercially produced visible-wave hollow waveguides. Commercial vendors can produce reasonable IR hollow waveguides, but visible-range waveguides exhibit high losses and high optical noise. The patented NETL Raman Gas Analyzer requires visible-range hollow waveguides with small internal diameters (a few hundred microns) and low optical noise. No vendor could produce these waveguides, so NETL constructed this new system of waveguide fabrication. Other spectroscopic systems would benefit from better waveguides including absorption spectrometers, microscopes, sensors, etc.


Researchers at NETL have developed method of fabricating a hollow glass waveguide of high optical quality that can be used in the visible or short-wave spectral regime for applications in Raman spectroscopy or laser beam delivery. To accomplish this, researchers have developed a system of electroless silver deposition that produces an optically smooth and highly reflective coating inside a hollow capillary tube with a small diameter. By controlling proves parameters like pressure, flow, and temperature in a carefully crafted pressurized deposition system, researchers can produce such coatings, despite the normal difficulties with coating technologies in small confined spaces like capillary bores.  Capillary waveguides produced with this method exhibit uniform coatings along the entire waveguide length to optimize the devices for visible light collection or transmission. Furthermore, the process results in waveguides that exhibit low levels of fluorescence or other unwanted noise for spectroscopic applications. This is accomplished via control of deposition parameters, chemical precursors, and dielectric protective materials over the internal metal coatings.  


  • Better transmission in the visible-wave regime
  • Improved optical collection in spectroscopic applications (capillary gas cells, etc.)
  • Improved visible laser beam delivery
  • Lower noise collection via materials selection



Applications of the NETL-developed method include fabricating high optical quality hollow waveguides that have very low fluorescence background, high signal-to-noise ratio, and very low loss in the visible range. The waveguides have applications in spectroscopy as well as in various medical procedures, pharmaceuticals, food & beverage, oil & gas, chemicals & petrochemicals, and water & wastewater management.

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