ABSTRACT
A standard tandem triple-pass scanning Fabry-Perot interferometer of the Vernier type for applications in the near infrared is described. The Fabry-Perot etalons have been coated with a specially designed dielectric multilayer stack with low loss factors and a uniform reflectivity of (92.5 +/- 1.0)% between 730 and 860 nm. The performances of the instrument, such as resolution, total transmission, and contrast, are equivalent to conventional tandem Fabry-Perot spectrometers but over the whole near-infrared wavelength range. Applications of the system to Brillouin scattering on semiconductors in the transparent wavelength regime and high-resolution spectroscopy of vertical cavity surface-emitting lasers are given.
ABSTRACT
A passive spatial light beam deflector based on a channel waveguide phased-array concept is presented. Diffraction gratings patterned by electron-beam lithography couple light into and out of the device. Phasing is achieved electro-optically with indium tin oxide/AlGaAs Shottky junctions. Discrete beam steering is first demonstrated with a 43-element rib waveguide array at an 850-nm wavelength. A sawtooth electrode keeps the device length short and the electrode surface small. Continuous deflection over a ±7.2 mrad range at a 900-nm wavelength is then reported. A set of seven sawtooth and offset electrodes permits addressing any point within this range. The beam has a width of 1.5 mrad, and the maximum modulation voltage is -8.5 V.
ABSTRACT
We characterize an AlGaAs rib waveguide using a structure based on a third-order Bragg reflector fabricated by electron-beam lithography. The grating forms a resonant cavity with the sample's uncoated output facet, and we observe a Fabry-Perot étalon behavior superimposed on the Bragg reflector characteristics. We present transmitted intensity measurements as a function of wavelength and temperature. We derive results for waveguide refractive-index profile, loss coefficient, group effective index, effective-index wavelength dispersion, and effective-index temperature dispersion. An auxiliary prism on top of the grating allows us to couple light out of the waveguide into the air. Angular measurements of the outcoupled orders at different wavelengths confirm the wavelength dispersion measurements made on the Fabry-Perot étalon formed by the grating and the cleaved mirror.
ABSTRACT
Low-loss (1.4-cm(-1)) single-mode rib waveguides in Al(x)Ga(1-x)As heterostructures are fabricated by liquid phase epitaxy, double anodization, and photolithographic techniques. Switching of optical channels between adjacent waveguides is accomplished with directional coupler switches controlled with electrodes laid over an isolating dielectric, making a metal-oxide-semiconductor (MOS) configuration. Complete switching is achieved with <20 V applied to a stepped Deltabetareversal electrode configuration. A 2 x 4 switching matrix with low-loss lateral offsets of the waveguides is demonstrated. By laying out several optical switching and guiding experiments within a 128-mum stripe, we show that independent optical circuits can be packed with adequate optical isolation using centerline separations approximately 10 microm.
