A pixellated grating array using photoelectrochemical etching on aGaAs waveguide

We have demonstrated and evaluated a grating array outcoupler fabricated by photoelectrochemical (PEC) etching, a manufacturable and practical approach for fabrication of grating-based III-V semiconductor waveguide devices. An array of submicron period gratings was etched into photolithographically delineated areas in a single PEC step. The fabricated devices are: 10-μm wide rib waveguides with 0.35-μm first-order outcoupling gratings; and 10-μm wide rib waveguides with 10 μm×10 μm pixellated areas of gratings. Device characterization demonstrates the effectiveness of outcoupling grating fabrication using PEC and that the pixellated grating outcoupler is an effective and simple means of generating an optical beam array     

Monolithic integration of 1.3-μm Stark-ladder electroabsorptionwaveguide modulators with multimode-interference splitters

In this letter, we describe a novel fabrication process for the monolithic integration of a waveguide power splitter based on the multimode-interference effect with multiple-quantum well (MQW) electroabsorption modulators based on the Stark-ladder effect. The integrated device is fabricated by a one-step epitaxy process using molecular-beam-epitaxy growth and three lithographic steps that eliminates the need for aligned regrowth of the MQW modulator. Experimental results of the modulation depth and wavelength dependence are also reported     

Spatial power splitting and combining based on the Talbot effect

The Talbot effect, a multimode interference phenomenon, is investigated as a technique for combining power from solid-state devices in order to generate higher levels of microwave and millimeter-wave power in a process referred to as quasioptical or spatial power combining. We explore the feasibility of using the Talbot effect to implement a 1 × 8 power splitter and an 8 × 1 power combiner at 94 GHz. We report the first demonstration of the multimode interface phenomenon in a planar waveguide at 8 GHz     

A manufacturable technique for implementing low-loss self-imagingwaveguide beamsplitters

A manufacturable technique to implement self-imaging waveguide beamsplitters is proposed and demonstrated. This technique offers low insertion loss and polarization crosstalk, uniform splitting ratios, ease in manufacture, and most importantly application to diverse waveguide material systems. Beamsplitters with splitting ratios that range from 1×2 through 1×17 were fabricated in GaAs-AlGaAs waveguides. For 1×16 splitters integrated with an output ridge waveguide array, the insertion losses in many devices were less than the insertion losses in adjacent straight-through ridge waveguides. The best uniformity spread among the 16 channels was 17.8% and the TE-to-TM and TM-to-TE polarization crosstalks were lower than -25 dB     

Clinical and genetic analysis of a distinct autosomal dominant spinocerebellar ataxia

OBJECTIVE: To characterize a distinct form of spinocerebellar ataxia (SCA) clinically and genetically. BACKGROUND: The SCAs are a genetically heterogeneous group of neurodegenerative disorders affecting the cerebellum and its connections. The mutations for SCA1, 2, 3, 6, and 7 have been identified and shown to be due to expansion of a CAG repeat in the coding region of these genes. Two additional SCA loci on chromosomes 16 and 11 have been designated SCA4 and SCA5. However, up to 20% of individuals with autosomal dominant forms of ataxias cannot be assigned any of these genotypes, implying the presence of other unidentified genes that may be involved in the development of ataxia. METHODS: We ascertained and clinically characterized a six-generation pedigree segregating an autosomal dominant trait for SCA. We performed direct mutation analysis and linkage analysis for all known SCA loci. RESULTS: The mutation analysis excludes SCA1, 2, 3, 6, and 7, and genetic linkage analysis excludes SCA4 and SCA5 (multipoint location scores < -2 across the candidate region). Clinical analysis of individuals in this family shows that all affected members have dysarthria, gait and limb ataxia, and nystagmus. No individuals have major brainstem or long-tract findings. Analysis of age at disease onset through multiple generations suggests anticipation. CONCLUSION: This pedigree represents a genetically distinct form of SCA with a phenotype characterized by predominantly cerebellar symptoms and signs.