Large Index Change Research Articles

InGaP/InP waveguides

We have made InGaP/InP waveguides on InP substrates by atmospheric pressure metalorganic vapor phase epitaxy. The introduction of Ga in the cladding layers causes a large relative index change (Δn=0 to >0.18) that can be varied with the Ga concentration (Δn=0.18 with Ga at 5×1019 cm−3), creating strong, low loss (∼1.25 dB/cm) waveguides. In addition some of these structures were doped with Fe, using ferrocene as the Fe doping source. Typical resistivities of 107 Ω cm have been achieved at Fe concentrations of 5×1017 cm−3, allowing electric fields in excess of 10 000 V/cm to be applied to the waveguides. InGaP/InP Fe-doped waveguides should prove extremely useful in fabricating switches, modulators, couplers, and filters for integrated optics devices.

Carrier-induced index change in AlGaAs double-heterostructure lasers

A large carrier-induced index change is reported for conventional 8 μm-stripe oxide-isolated AlGaAs double-heterostructure lasers. At threshold, the index change of the active layer is −0.05 to −0.07, which is a factor of 5 to 10 larger than previously reported. It is accompanied by an even greater change in dispersion. These effects cannot be explained by a free-carrier effect, and are most likely caused by a carrier-induced shift of the absorption edge.

Oxide optical memories: Photochromism and index change

Due to the many valence states available to transition element ions, transition element oxides doped with these impurities are particularly useful for optical storage. Either the color (as in SrTiO 3) or refractive index (as in LiNbO 3) of these materials can be changed by exposure to light. Color change (photochromism) involves optically induced oxidation-reduction effects that can also be produced by electrochromic treatments. Large index change occurs in electrooptic crystals, and is due to the optical generation of internal space charge fields. The latter process is highly useful for bulk hologram storage, particularly since the resulting holograms can be fixed by a simple heat treatment. The mechanisms and capabilities of these processes will be discussed with emphasis on photochromism and electrochromism in Ni,Mo doped SrTiO 3; and hologram storage in Fe doped LiNbO 3.

The Measurement of Homogeneity of Optical Materials in the Visible and Near Infrared

A procedure is described for determining the inhomogeneities of a sample of optical material in terms of small changes in index of refraction at discrete points over the measured surface. The method is used in the visible- and near-ir regions of the spectrum. An He-Ne gas laser source was used for the ir measurements. The variation in index was mapped with contour lines enclosing areas of similar index variations. The largest index change in 1-cm distance was noted and recorded as the maximum variation per centimeter. Over twenty-five different samples of six different materials were examined. The results are presented in a chart indicating the range of maximum refractive index variations of the samples observed. Data are shown to illustrate the possibility of determining index values to higher precision than the material justifies.