a) Schematic of the HPCVD process, where a high pressure precursor mixture is configured to flow into a capillary (left). When the capillary is heated, well-developed annular films are deposited. Unreacted precursors, carrier gas, and reaction byproducts are carried out of the fiber (right). b) Diascopically illuminated optical micrograph from the side showing the transparent, uniform ZnSe fiber core. The deposited structures can have a uniform cross section for as long as 4 cm when made in a 10-cm-long furnace. Note that cylindrical lensing effects magnify the interior tube diameter considerably in this view, making its 400 nm diameter appear much larger than it is. c) Cross-sectional SEM image showing an overview of the silica cladding and ZnSe core. d) A higher magnification SEM image of the nearly completely filled core. Scale bars: b) 50 μm, c) 50 μm, d) 5 μm. Credit: J. Badding, PSU; Advanced Materials.
Scientists at Penn State University report that they developed the first optical fiber made with a core of zinc selenide. The team is led by John Badding, professor of chemistry at PSU with help from fellow researchers at the school’s Materials Research Institute and Department of Materials Science and Engineering, as well as scientists at the Optoelectronics Research Centre at the University of Southampton (U.K.).
Badding says in a PSU news release:
“It has become almost a cliche to say that optical fibers are the cornerstone of the modern information age. These long, thin fibers, which are three times as thick as a human hair, can transmit over a terabyte — the equivalent of 250 DVDs of information per second. Still, there always are ways to improve on existing technology. Glass has a haphazard arrangement of atoms. In contrast, a crystalline substance like zinc selenide is highly ordered. That order allows light to be transported over longer wavelengths, specifically those in the mid-infrared.”
The group’s methods include a specially developed high-pressure chemical vapor deposition technique. “The high-pressure deposition is unique in allowing formation of such long, thin, zinc selenide fiber cores in a very confined space,” Badding says in the release.
According to the PSU release, “this new class of optical fiber allows for a more effective and liberal manipulation of light and promises to open the door to more versatile laser-radar technology.” Other applications include the development of improved surgical and medical lasers, better countermeasure lasers used by the military, and superior environment-sensing lasers for measuring pollutants and to detect the dissemination of bioterrorist chemical agents. New lighting uses also may be possible.
ACerS member Venkatraman Gopalan, professor at Penn State’s Department of Materials Science and
Gopalan
Engineering and the associate director for the Center for Optical Technologies, is a member of the research team. In an email, Gopalan fills me in more about the context of their optical fiber discovery. He notes, “Infrared wavelength range is extremely important, and yet even the basic infrared technologies such as optics, coatings, waveguides, lasers, and detectors are in their infancy, as compared with technologies in the visible or telecon wavelengths. This development breathes new life into glass fibers that are usually infrared opaque beyond ~2.5 microns wavelength.”
He also predicts that these fibers could revolutionize many important areas of optics research, such as fiber-based guiding, imaging, spectroscopy and tunable lasers. “The deposition technique is versatile enough to imagine a whole family of important compound semiconductors making their way into fiber cores in the near future. Optical fibers may soon come with many flavors and functions well beyond what glass can do,” writes Gopalan.
Researcher team member Anna Peacock remarks on her website that, “ultra-fast all-fibre optical switches will reduce costs and improve efficiency of communications systems, whilst laser sources, which operate in the mid-infrared, can be used for environmental sensing and medical applications. The incorporation of the active semiconductor component into the fiber geometry provides an important step towards seamlessly linking semiconductor photonics with existing fiber infrastructures.”
The team’s research was published online March 1, 2011 in the Early View version of Advanced Materials.
This recent work seems to follow a logical progression of research efforts by many of the team members. Baddin, P.J.A. Sazio and Gopalan demonstrated that they could build semiconductor devices (germanium) in optical fibers in 2006 and predicted then that this would lead to fibers with flexible waveguides. That year, they also demonstrated similar techniques using optical fibers with special microstructure features.
In 2007, the group also published a paper on filling microstructured optical fibers with amorphous silicon and built on this in 2008 by showing how they could use a high-pressure microfluidic process to adapt traditional chemical vapor deposition techniques to deposit silicon carbide in MOFs. Their thinking then was that “the introduction of SiC into the capillaries presents tremendous potential for the development of in-fiber optoelectronic devices with potential applications, including light generation, modulation and amplification.”
By 2010, they were able to produce silica nanofibers with circular cross sections that can simultaneously waveguide transverse electric and transverse magnetic polarizations without cutoffs.