D. A. Pinnow

Fundamental optical attenuation limits in the liquid and glassy state with application to fiber optical waveguide materials

Fundamental optical scattering and absorption mechanisms have been identified which limit light transmission in fiber optical waveguide materials. These mechanisms, which are intimately associated with the random structure in the liquid and glassy state, are described and then used as a basis for comparing fiber optical waveguide materials. It is concluded that pure fused silica is a preferred waveguide material, having ultimate total losses of 1.2 dB/km at the Nd : YAG laser wavelength of 1.06 μ, 3.0 dB/km at the GaxAl1−xAs emission wavelength of approximately 0.8 μ, and 4.8 dB/km at the GaP : Zn, O emission wavelength centered at 0.7 μ.

Development of a Calorimetric Method for Making Precision Optical Absorption Measurements

Present trends toward the development and application of exceptionally high quality optical materials have made requirements on optical loss so stringent that they exceed the capabilities of existing measurement techniques. This work describes a calorimetric method for determining optical absorption in bulk materials which is over an order of magnitude more sensitive than previous methods. The large circulating optical power within a laser cavity is used to heat a small rod shaped sample of test materialplaced within the cavity. The optical absorption within the sample causes its temperature to increase until the absorbed power is balanced by heat leakage out of the rod. To minimize this leakage, the rod is thermally isolated from its surroundings. The optical loss in the sample can be calculated knowing the optical power passing through it, its temperature rise, and the cooling time constant which is determined by abruptly turning off the laser. Losses as low as 2.3 +/-0.5 dB/km at 1.064 micro have been measured with high reliability.

LEAD MOLYBDATE: A MELT‐GROWN CRYSTAL WITH A HIGH FIGURE OF MERIT FOR ACOUSTO‐OPTIC DEVICE APPLICATIONS

Crystalline lead molybdate PbMoO4 has been found to be well suited for acousto‐optical device applications. This material has desirable properties similar to the previously reported α‐iodic acid α‐HIO3. However, PbMoO4, unlike α‐HIO3, is insoluble in water and can therefore be readily fabricated into devices and its optical surfaces do not require protection from the atmosphere. The elastic, photoelastic, optical, and thermal properties of PbMoO4 have been measured. These data have been used in the design of several acousto‐optic devices. An example consisting of a two stage (horizontal and vertical) acoustically driven light deflector is described. Each stage of this deflector has an 80‐MHz bandwidth and can deflect over 50% of an incident laser beam (5145 A) with less than 1 W of electrical drive power.

Total Optical Attenuation in Bulk Fused Silica

A survey has been made of optical attenuation in a series of commercially available silica, SiO2, samples to determine the suitability of this material for fiber optical communications. The absorptive component of the attenuation was measured by a precision calorimetric technique, while the scattering component was determined by a new method based on spontaneous Brillouin spectroscopy. Both techniques set an upper limit on the loss and are precise to within a fraction of 1 dB/km. Of the samples tested, the best has a total attenuation of less than 3 dB/km at the 1.06‐μ wavelength of the YAlG : Nd laser.

Borosilicate glasses for fiber optical waveguides

Abstract Of the existing optical glasses, pure fused silica is known to have the lowest optical attenuation in the red and near infrared portion of the spectrum where optical communications appears most promising. However, to approach the low attenuations afforded by pure fused silica in a waveguide structure requires that a core of fused silica be clad with a glass of slightly lower index refraction. This paper describes an investigation of the binary borosilicate glass system which has led to the realization of a promising cladding material for pure fused silica core fibers.

Low‐loss silica core‐borosilicate clad fiber optical waveguide

A low‐loss fiber optical waveguide has been constructed having a pure fused silica core of 40‐μm diameter and a chemical‐vapor‐deposited cladding layer of borosilicate glass 15–20 μm thick. This core‐clad structure has an outer jacket of fused silica which serves to strengthen and protect the waveguide. Fabrication procedures and evaluation techniques are described. One fiber has been found to have a minimum optical attenuation of 13 dB/km at a wavelength of 0.7 μm. In the range 0.8–1.1 μm, where optical communications appear most promising, the attenuation varies between 18 and 22 dB/km with the exception of the OH absorption peak at 0.95 μm.

LOW ACOUSTIC LOSS CHALCOGENIDE GLASSES— A NEW CATEGORY OF MATERIALS FOR ACOUSTIC AND ACOUSTO‐OPTIC APPLICATIONS

Some ternary groups 1VA‐VA‐V1A nonoxide glasses have been found which have very low acoustic losses of the order of fused silica, low values of sound velocity, and very high acousto‐optic figures of merit. Their optical transmission range is 1 – 12μ. The unusual combination of these parameters in a chemically stable isotropic medium make these glasses attractive for us in acoustic and acousto‐optic devices operating at infrared wavelengths.

Binary SiO2–B2O3 glass system: Refractive index behavior and energy gap considerations

A recent investigation of the binary borosilicate glass system has led to the realization of a useful cladding material for pure fused silica core fiber optical waveguides. The feature which makes the borosilicate glass useful is that its index of refraction is sufficiently less than that of pure fused silica to allow light guidance in silica core‐borosilicate clad fibers. The previous work offered no explanation for the observed but unexpected behavior of the borosilicate refractive index. Continued studies of this glass system have now led to a quantative explanation of the refractive index behavior. Two theoretical approaches are discussed. One is based on the Sellmeier dispersion model and the other on a molar refractivity analysis. The main quantities of interest turn out to be density, composition, structure, and ionicity. An important prediction based on this work is that properly quenched borosilicate glass can have a refractive index even lower than previously observed. This prediction was subseq...

Investigation of the soda aluminosilicate glass system for application to fiber optical waveguides

Abstract An extensive investigation of the soda aluminosilicate glass systems has been conducted to determine the suitability of this material for low loss fiber optical waveguides. Based on measurements of scattering loss energy gap, and glass transition temperature we conclude that certain compositions of soda aluminosilicate glass have substantially lower measured scattering loss and less estimated absorption loss than pure fused silica, the best of the present waveguide materials. Scattering losses less than 1 4 that of pure fused silica have been observed.

Evaluation of Fiber Optical Waveguides Using Brillouin Spectroscopy

Optical scattering loss in fiber optical waveguides is the sum of the bulk material scattering and excess scattering loss due to imperfections in the waveguide structure. The recently developed Brillouin spectroscopic technique for evaluating bulk scattering has been extended to fiber waveguides, and a detailed investigation has been performed on a borosilicate clad-pure fused silica core waveguide. The technique has been found to be useful in evaluating scattering due to waveguide imperfections that have been determined to occur at the core-cladding interface. In addition to providing a measure of the waveguide scattering loss, the Brillouin technique has also been found to be useful in determining the molar composition of the borosilicate cladding glass and the partition of guided optical power between the core and cladding regions. The unusual capabilities of this technique should make it generally useful for characterizing integrated optical structures.