Photoelastic waveguides formed by interfacial reactions

Abstract

The fabrication of low-loss photoelastic waveguides in GaAs/AlGaAs layered structures by thin film reactions is investigated. The waveguides are formed by opening a narrow window stripe, a few microns wide, in an otherwise continuous Ni layer under tension deposited on a semiconductor structure. The local tensile stress induced by the Ni layer in the semiconductor causes the local refractive index to increase, thus providing the guiding mechanism. Annealing the sample at 250 °C for 1 h induced an interfacial reaction between the Ni film and the substrate to form Ni3GaAs. The formation of an interfacial compound stabilizes the stresses, making the stress state independent of the deposition system and technique. Single-mode waveguide propagation losses as low as 1.4 dB/cm at 1.53 μm wavelength have been obtained on annealed waveguides. Further annealing up to 600 °C did not cause degradation in the optical confinement, thus indicating a thermally stable planar waveguide fabricated by this process. Other photoelastic optical devices such as polarizers, splitters, and couplers are also demonstrated.

Polarized cathodoluminescence for strain measurement

“…Furthermore, two images of the polarized intensity are taken, one before that of the ∥ polarized intensity and one after; the two images are geometrically averaged before DOP calculation using Eq. (5). In Cassidy's PL tool, 29 although sample charging is not an issue, a rotating polarizer enables simultaneous acquisition of I and I ∥ , thus avoiding drift issues.…”

“…4 Photoelastic optical waveguides have also been developed. 5 Strain can arise from a lattice 6 or a thermal expansion mismatch between two deposited layers as well as from soldered or glued packages. 4 Techniques for the measurement of strain in crystalline materials include X-ray diffraction (XRD), 6,7 Raman spectroscopy, 8 transmission electron microscopy (TEM), 9,10 and scanning electron microscope (SEM)-based electron back scatter diffraction (EBSD) 11 each having strengths and limitations in terms of spatial resolution, field of view, sensitivity, accuracy, and ease of use.…”

Photoelastic waveguides formed on bulk GaAs or Si

“…Semiconductor waveguides that utilize the thin-film induced stress, so called semiconductor photoelastic waveguides, have been reported by many workers. To the author's knowledge, however, the photoelastic effect in semiconductors has been utilized only for the lateral confinement of light, not for the vertical confinement [1,2,3]. For the vertical confinement of light, people normally use a layered structure that has a higher-refractive-index guiding layer sandwiched by lower-index cladding layers.…”

Photoelastic waveguides induced by a thin-film composite structure in InGaAsP/InP double heterostructures

“…Recently, a stable distribution of stress in AlGaAs/GaAs double heterostructures has been obtained by either metalsemiconductor interfacial reactions or rf sputtered refractory metal film with dc bias on the substrate [4]. By using this technique, planar photoelastic AlGaAs/GaAs quantum well lasers [5], photoelastic modulators [6] and planar photoelastic directional couplers [7] are created. Previously, Kirkby et al [3] proposed four possible configurations for producing a useful photoelastic waveguide: (i) a wide (more than 15 µm in width) stripe window in a film under compression, (ii) narrow (a few µm in width) stripes of film under compression, (iii) wide (more than 15 µm in width) stripes of film under tension and (iv) a narrow stripe (a few µm in width) window in a film under tension.…”