Developments in New Optical Materials

Developments in New Optical MaterialsSolomon MusikantGENERAL ELECTRIC COMPANYSPACE DIVISIONP.O. BOX 8555, Philadelphia, PA 19101 USAAbstractThis paper is a review of current developments in new optical materials based ona survey of the recent literature. Rapid advances are taking place in the fields of passiveand active optical materials. Among the former are new optical fibers and refractivematerials suitable for excimer lasers. Among the latter are electrooptic crystals ofmany varieties including liquid crystals and molecular non -linear materials. Among thekey application areas are optical fibers waveguides, optical storage, and optical dataprocessing devices. Several examples of each of these new areas will be mentioned inthe paper.Optical glasses - generalGliemeroth(1) has outlined the trends in the development of new optical glasses. Figure1 lists these trends. The demand for achromatization of glass optics is leading to thedevelopment of two new groups of glasses situated on the index of refraction Abbe numberchart as shown in Figure 2. In addition, due to environmental problems, the elementsthorium and cadmium are being eliminated by substitutions of Nb, Ti, Gd and Zr leadingto new optical glasses. In addition the partial substitution of fluorine for oxygen isproducing optical glasses with unique properties.Improvement in chemical durability of optical glasses has been driven by the desireto reduce production costs associated with polishing operations. Alkali resistant glasseshave therefore been developed.The work in developing ultra low absorption fiber wave guide glasses is being trans-ferred to bulk glasses. As a result bulk glasses with significantly lower absorptioncoefficients are now available. Such high transmitting glasses are produced from speciallycleaned raw materials. As a result, complex optical trains containing up to twenty lensesare appreciably better.Optical light weight glasses have become available by the introduction of titaniumoxide and zirconia which led to lower density alternates to various glasses in the indexof refraction Abbe number chart. By the use of such glasses, weight reductions up to30% were achieved without recalculation of the optical systems.For various applications, especially fluorescent microscopy, the elimination of fluo-rescent species is needed. Therefore, a series of glasses has been developed which avoidsuch fluorescence. A similar development has taken place with respect to solarizationof glass, that is the darkening of glass under visible and ultraviolet light, and evenglasses resistant to gamma radiation are now available.At the other end of the spectrum, there are active programs to find infrared transmittingbulk materials in the 5 to 20 micron transmitting range which have low absorption coefficientand high mechanical strength. Such materials have been described recently by Rhodes etal(2), Hartnett et al(3), Saunders et al(4), Covino(5,6), Musikant et al(/), and Riceet al(8). These materials are respectively Y2O3, AlON (aluminum oxy nitride), CaLa2S4,and more recently ZnGeP2 and ZrO2.Optical fibersSilica has reached a very high level of development for optical fibers even for longdistance transmission. However, there is a promise for an order of magnitude or betterimprovement in absorption and scattering losses by going to higher infrared transmissionthan currently employed. A very active development thrust is now ongoing to perfect infraredtransmitting fibers such as the zirconium fluorides. The higher infrared transmissionoffers a significant reduction in Rayleigh scattering. However, much work still has toaccomplished to achieve the mechanical strength and environmental resistance needed tobe suitable for long distance transmission lines. This work has recently been summarizedin Bendow(9).