Optical Materials. Technology Development

Optical materials were essential for many of the twentieth century’s most significant technological accomplishments. Humans have been intrigued with the development of optical materials and light behavior for centuries. Thomas Alva Edison, Max Planck, Albert Einstein, Max Born, and Niels Bohr presented significant optical theories and innovations that provided a foundation for research, development, and application of twentieth century optical materials.

Significant optical milestones included the introduction of lens coating in the 1930s and lasers in 1960; fiber optics emerged by mid-century, and thousands of scientists innovated and adapted uses for optical materials in the following decades. Engineers established the International Society for Optical Engineering (SPIE) in 1955 to coordinate professional efforts.

During the 1870s, German chemist Dr. Otto Schott sought to make glass with optical qualities, devising a lithium formula. By 1884, he produced optical glass specifically for lens and prism applications such as microscopes. With colleague Dr. Ernst Abbe and industrialist Carl Zeiss, Schott established the pioneering optical glass-manufacturing site at Jena, Germany. As a result, Germany was the main manufacturer of optical glass prior to World War I.

Initially, scientists were most concerned with the composition of optical glass. The production of optical glass and removal of impurities is crucial to achieve optimal performance. The homogeneity of optical glass differentiates it from most glass. Its consistent, predictable quality; strength and durability despite physical stresses and temperatures; precise images; minimization of distortion; and versatility for desired applications all make it ideal for optical usages.

In the early twentieth century, German technologists advanced optical glass technology with such innovations as Schott’s borosilicate and barium glass. By 1939, George W. Morey of the U.S. devised optical glass composed of tantalum, lanthanum, and thorium that increased refraction.

Before World War II, most optical glass manufacture resulted from clay pot melting processes. After the war, technologists focused on manufacturing aspects to improve optical glass. Some technicians used platinum pots and rare earth elements to create optical glass with minimal flaws (such as bubbles, weaknesses, and striae) where refraction differed. Japanese technologists at Hoya Corporation initiated a continuous melting technique in 1965 that produced flaw-free optical glass.

Engineers worldwide devised better materials and melting processes, including electric melting, to create optical glass for electronics and cameras that were becoming lighter, smaller, and more precise because of optical glass lens advancements. Most modern optical glass is made from fused silica that is synthetically manufactured to enhance purity and quality.

In 1938, American Katherine J. Blodgett patented a layered soap film to produce transparent glass that did not reflect light rays and distort images in lenses because the soap and light waves neutralized each other. Her findings inspired optical coating work to apply transparent thin films to lenses, glasses, and electronic devices. Scientists developed materials especially for those purposes. Most modern optical coating materials are metals, semiconductors, or insulators.

In the late twentieth century, plastic lenses replaced eyeglass lenses. In addition to being more shatterproof, plastic material such as polycarbonate enables technicians to apply or incorporate a wider variety of optical technology, primarily in coatings, to enhance vision. Each side of a plastic lens is layered with thin films that aid in making the lens invulnerable to water, glares, and scratches.

A physical vapor deposition technique is used for the antireflective coating in which such metal compounds as aluminum oxide undergo vaporization in a vacuum chamber and several layers of atoms are deposited on a lens. A hydrophobic coating is layered on the lens by chemical vapor deposition or submersion in a solution. Engineers improved coatings that protect eyes from ultraviolet light.

The transparent vinyl thermoplastic polymer polymethylmethacrylate (PMMA) was first industrially produced in the mid-1930s after chemists initiated research the previous decade. PMMA is commonly referred to as acrylic, a word derived from the name acrylates, the polymer family that includes PMMA. This hard synthetic plastic cannot be shattered like glass and is used for various optical needs.

In 1928, the company Rohm & Haas (based in Philadelphia and Darmstadt) began to sell acrylics based on resins made by Rudolph Fittig in the nineteenth century and adapted by German chemist Otto Rohm, for coating use as a celluloid substitute. At Imperial Chemical Industries, English chemists John Crawford and Rowland Hill made a harder acrylic in 1934 in a heating, pouring, baking, and cooling process to create acrylic sheets that were marketed as Perspex.

Competition between acrylic manufacturers resulted in improved acrylic production methods and applications. Acrylic is more vulnerable to impact damage than polycarbonate in lenses, but PMMA is considered a valuable optical material for its superb clarity, electrical characteristics, and resistance to scratching. Engineers developed computer-guided looms to weave acrylic optical fibers. Acrylic is also used for LED and other optical displays. Lucite (DuPont) and Plexiglass (Rohm & Haas) are well-known trade names for acrylic optical products.

Because of its lightness, flexibility, affordability, and ability to be tinted with color, plastic is often shaped to make contact lenses. Leonardo da Vinci first suggested contact lenses in the early sixteenth century, and scientists developed similar glass lenses in the following centuries. In the mid- 1930s, American Dr. William Feinbloom created hard plastic contact lenses. Californian Dr. Kevin Tuohy received a PMMA corneal contact lens patent in 1950.

Industries such as Bausch and Lomb produced lenses, and researchers improved designs to resolve problems patients reported. English ophthalmologist Harold Ridley innovated the intraocular lens (IOL) in 1949 for lens replacement in cataract surgery. Although PMMA is used for IOLs, chemists developed softer acrylics and silicones that can be folded to insert in smaller eye incisions than required for PMMA IOLs.

Softer plastics gradually replaced PMMA as a lens material except for specific uses such as treating astigmatism. By the 1960s, contact lenses became more appealing when Czechoslovakian optometrists Otto Wicherle and Drahoslav Lim used the polymer hydroxyethylmethacrylate (HEMA) to make soft contact lenses. They selected materials that can absorb moisture to become flexible. By 1979, rigid gas-permeable (RGP) contact lenses containing primarily silicone (which permits oxygen to reach the eyes) were introduced.

RGPs often correct vision problems that soft lenses cannot, last longer, and do not collect as much debris as soft lenses. Technological advancements in contact lenses included bifocals, disposable contacts, and improved material formulas that resulted in thinner lenses and increased oxygen access to the eyes.

Fiber optics enable telecommunications to span the globe swiftly and clearly. Glass fibers transmit infrared light pulses that are sounds or digital information transformed into light by semiconductor lasers. Optical fibers, made of a core inside a separate glass cladding, consist primarily of extremely pure silica.

Scientists add fluorine and boron to the cladding and phosphorous and germanium to the core to manipulate those components’ refractive index as needed for efficient light movement through fibers. The cladding prevents light from leaking out of the core by reflecting light within the boundaries of the core (total internal reflection).

Visionaries who proposed fiber optic technology in the 1920s and 1930s but did not follow through with their ideas included American Clarence Hansell, who received a patent for bundling glass fibers, and German Heinrich Lamm, who experimented with glass fibers for surgery. Narinder S. Kapany is often credited as fiber optics’ inventor, but his Massachusetts Institute of Technology doctoral advisor, Harold H. Hopkins, suggested Kapany’s topic.

Hopkins had been investigating glass fibers and wanted to bundle them to transmit images when he received a grant which he used to hire Kapany. The initial letter describing their work was published in Nature on 2 January 1954 beneath a letter about fiber bundling that Dutch scientist Abraham C.S. van Heel had submitted months before. Kapany wrote a Scientific American feature in 1960 and the first book on that topic.

Dr. Charles K. Kao is also cited as the innovator of fiber optics because of his research at the English ITT Standard Telecommunications Laboratories in the 1960s. Kao and Charles Hockham wrote about fiber optic possibilities. Kao was particularly interested in purifying optical materials such as silica compounds to remove metal impurities and improve transmissions. During the early 1970s, Corning Glass Works researchers Robert Maurer, Don Keck, and Peter Schultz developed a heat process to make extremely clear glass fibers from fused silica doped with germanium.

Their achievement resulted in fibers with much lower attenuation (power loss with distance along the fiber), and fiber optic communications became feasible. Losses in optical fibers were much lower than in copper cables, and fewer repeaters meant lower cost systems. At the same time, researchers developed semiconductor lasers for use as fiber-optic light sources.

In addition to these pioneers, since the 1960s, many people and corporations, often fiercely competing to secure patents, have contributed to the advancement and distribution of fiber optics worldwide. Some researchers focused on multimode optic fibers instead of single-mode fibers, delaying the technology in some regions because of interference and noise caused by conflicting modes and waves that can disrupt transmissions.

Toni Karbowiak’s 1964 waveguide aided acceptance of optical fibers when they first became publicly available in the 1970s. On 19 May 1971, Queen Elizabeth II observed a fiber-optic video presentation, and other trials were held in the U.S. By 1975, a pioneering fiber-optic system was in use for communications by police in Great Britain. Engineers at British Telecom, Bell, and GTE introduced fiber optics into their systems.

Researchers advanced fiber optics quickly in the 1980s, improving services particularly for longdistance telephone calls. International service advanced in 1988 with the introduction of TAT- 8, the initial transatlantic fiber-optic cable that provided increased circuits, greater capacity, and clearer signals than satellite and wire connections. More fiber-optic cables connected continents, with each fiber capable of transmitting several hundred million bits every second. During that decade, the University of Southampton’s Dave Payne realized erbium would be the most useful amplifier material in fibers for clear, uninterrupted signals transmitted via ocean cables.

Fiber optics reduced the need for amplifiers due to attenuation. Unless water vapor is present, most silica in optic fibers does not absorb material sufficiently to interrupt signal movement. At higher wavelengths, silica is prone to absorb material, and substitute fiber sources such as fluorozirconate are often used. Engineers focus on solving dispersion problems related to silica interaction with frequencies when various parts of a signal move at different speeds in fibers toward receivers, as this often creates pulse interference.

Researchers are constantly advancing fiber-optic materials, systems, and applications to achieve greater speed, amount of information transmitted, and practical uses. For example, fiber optics enables surgeons to access and examine internal organs without performing surgery.

Fiber optics help guide missiles, find earthquake victims, provide transportation signals, and act as sensors. Although many communities’ telephones, Internet, and cable television services relied on fiber-optic networks, because such technology is expensive, few private homes had optic fibers by the end of the twentieth century and were connected to those systems by wires.