F. W. Ostermayer

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.

Infrared‐to‐Visible Conversion by Rare‐Earth Ions in Crystals

An analysis of infrared conversion to visible and ultraviolet radiation by Yb3+–Er3+, Yb3+–Ho3+, and Yb3+–Tm3+ ions in crystals is presented. The expression for the visible power output in the presence of back transfer from the active ion to the energy‐transferring ion (Yb3+) is given and the relationship between the intermediate state transfer and back transfer coefficients for maximum output is found. If this relationship is satisfied the visible output in the presence of back transfer is equal to the maximum output with no back transfer. The behavior of the power output when the transfer and back transfer coefficients depart significantly from this optimum condition is examined and the parameters which govern the power output under these conditions are determined. The analysis is applied to Yb3+–Er3+, Yb3+–Ho3+, and Yb3+–Tm3+ ions in BaYF5 and BaY2F8. Measurements on the brightest composition of Yb3+–Er3+ ions in BaYF5 indicate that the advantage of a long‐lived intermediate state is diminished by back...

Photoelectrochemical etching of integral lenses on InGaAsP/InP light‐emitting diodes

A photoelectrochemical method has been developed for etching integral lenses on light‐emitting diodes (LED’s). An LED wafer is immersed in an electrolyte and biased at a potential at which the etch rate is directly proportional to light intensity. The image of a photomask is projected onto the surface of the wafer to produce a spatial variation of light intensity to etch the desired shape. The method has been used to etch spherical lenses on the n‐InP substrates of InGaAsP/InP LED’s. Extremely smooth surfaces are obtained for etch rates ≲0.5 μm/min. The resulting lensed LED’s gave the theoretically expected improvement in the light coupled into an optical fiber, indicating that the scattering loss of the lenses was very small. The technique is compatible with the standard LED processing and the apparatus required is relatively simple.

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.

Efficiency of Red, Green, and Blue Infrared‐to‐Visible Conversion Sources

Efficiencies of ∼1%, 0.1%, and 0.01% have been achieved, respectively, in the red, green, and blue with simple infrared‐to‐visible conversion sources. Saturation effects observed in the blue‐emitting phosphor Y0.65Yb0.35Tm0.001F3 have been explained. The first and second cross‐transfer coefficients for this Yb, Tm system have been determined to be 1.3×10−17 and 8.3×10−15 cm3 sec−1.

Holographic photoelectrochemical etching of diffraction gratings in n-InP and n-GaInAsP for distributed feedback lasers

Direct photoelectrochemical (PEC) etching of diffraction gratings on n‐InP and n‐GaInAsP in a 2‐M HF/0.5‐M KOH solution has been demonstrated using laser interference holography. Development of a maskless technique for producing gratings has potential application in the fabrication of distributed feedback lasers which are currently made by a multistep photoresist process. Submicron diffraction gratings having a period of 0.5 μm, corresponding to second‐order feedback in GaInAsP at λ=1.55 μm, have been achieved. Measurements were obtained on the exposure characteristics, diffraction efficiency, and PEC etching sensitivity of gratings produced in InP and GaInAsP as a function of the writing beam intensity, laser wavelength, material doping level, and grating spatial frequency. For grating frequencies greater than 100 mm−1 the sensitivity was observed to decrease approximately as the inverse square of the spatial frequency. In addition, undoped InP and GaInAsP exhibited significantly lower sensitivities than...

Room‐Temperature cw Operation of a GaAs1−xPx Diode‐Pumped YAG:Nd Laser

Room‐temperature (20°C) cw operation of a YAG: Nd laser pumped by GaAs1−xPx electroluminescent diodes is reported. A linear array of sixty‐four 0.46‐mm‐diam domed diodes was coupled to a 1.5‐mm‐diam × 50‐mm‐long laser rod by a semielliptical cylindrical reflector. At an electrical input to the diode array of 30 W, the optical pumping power was 0.90 W (average diode efficiency ≈ 3%) and the laser output power was 1.4 mW. The laser was also operated with 1‐ and 2‐msec pulses of pump power. At an electrical input of 30 W, the laser output at the end of a 1‐msec pulse was 4.9 mW, and at an electrical input of 44 W, the output was 15.7 mW. The discrepancy between the pulsed and cw output powers has been attributed primarily to heating effects in the diodes. When the laser rod was cooled to 0°C, the pulsed output at an input of 44 W was 55 mW.

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.

Using focused ion beam damage patterns to photoelectrochemically etch features in III‐V materials

A method of patterning n‐type GaAs, InP, InGaAs, and InGaAsP by photoelectrochemical (PEC) etching in conjunction with a submicron focused ion beam (FIB) at low dose is described. The ion beam is used to produce damage in a desired pattern in the material. Subsequent PEC etching of the material reveals the ion induced features in relief. The procedure is highly sensitive, requiring a dose of only 5×109 ions/cm2 for the differential etch to become apparent. The sensitivity allows rapid pattern generation in our FIB system.

GaAs1−xPx DIODE PUMPED YAG: Nd LASERS

Experiments using GaAs1−xPx diodes emitting at 8100 A to cw pump YAG: Nd laser rods are described. At an electrical input power of 7.6 W to an array of 4% efficient diodes operating at room‐temperature threshold was attained for a laser rod, with high‐reflectivity mirrors, cooled to 3.5°C. For a laser rod with a 0.4% transmission output mirror threshold was reached at −2.5°C. From threshold‐temperature‐dependence data for the latter rod, an extrapolation has been made showing that a straightforward increase in the number of diodes by a factor of 3 to 4 will result in threshold being exceeded by 2 to 3 times at a rod temperature of 20°C.