Biomedical subjects

Andrew G Kirk

Publications and source records attributed to Andrew G Kirk.

11 recordsLinked to original sources

PubMed2006

One-dimensional to two-dimensional channel formatting with micro-optics for wavelength division multiplexing networks.

We present a method of interfacing a conventional wavelength multiplexing and demultiplexing device with a two-dimensional (2-D) array of surface-active elements, such as micro-electromechanical system devices or photodetectors. We use diffractive optical elements to transform wavelength division multiplexed signals spread along a line into a 2-D array. We applied this technique to build a device that is compatible with an arrayed-waveguide grating. The theoretical insertion loss predicted by combining beam propagation and rigorous coupled-wave analysis is 2.75 dB. However, the experimental loss is 10 dB. The difference is due to the poor quality of the diffraction gratings. Nevertheless, the formatting operation was performed successfully.

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PubMed2005

Compact double-grating coupler between vertically stacked silicon-on-insulator waveguides.

We analyze a compact double-grating coupler that provides coupling through radiation modes between two vertically stacked silicon-on-insulator waveguides. The grating is sufficiently strong to be considered a one-dimensional photonic bandgap structure that facilitates a short coupling length. Simulations suggest that a 29% coupling efficiency is achievable in coupling light from one waveguide to another with 12.9 microm long binary gratings. We found that the coupling efficiency is enhanced by Fabry-Perot resonance between two gratings. The coupling efficiency can be increased by use of a blazed grating. We use the eigenmode expansion method to design and optimize the binary grating coupler, and the results are verified by use of the finite-difference time-domain method.

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PubMed2005

Rigorous coupled wave analysis applied to transmission efficiency of diffractive beam array relays for free-space optical interconnects.

Parallel high-density free-space optical interconnects typically relay multiple channels in an array configuration; thus, they require good uniformity across their aperture for optimum performance. Rigorous coupled wave analysis is used to determine the throughput off-axis diffraction efficiency for Fresnel lenses within a diffractive imaging relay. The rigorous results are compared with scalar theory and show a significant nonuniformity not predicted by scalar theory. However, the polarization sensitivity is found to be negligible for the f-numbers considered (f/2.9 to f/10.2). These results are supported by experiment.

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PubMed2004

Nonlinear frequency conversion in waveguide directional couplers.

Nonlinear optical effects for frequency conversion require a phase-matching condition to efficiently generate a coherent field at the new wavelength. We find that the phase-matching condition can be replaced by a resonance condition when the nonlinear effect takes place in a waveguide directional coupler. We apply this theory to second-harmonic generation and find a theoretical conversion efficiency of 100%, equivalent to the perfect phase-matching condition. An example of the design of such waveguide directional coupler is presented.

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PubMed2004

Six-degrees-of-freedom alignment technique that provides diagnostic misalignment information.

We introduce a new six-degrees-of-freedom alignment technique that enables the precise alignment of two optical device planes. The method combines linear diffraction gratings and cylindrical Fresnel lenses that allow the diagnosis of misalignment in each degree of freedom independently. The technique was used to align two 20 mm x 20 mm fused-silica substrates separated by 17 mm. The worst-case alignment precision was found to be better than +/- 5 microm laterally, +/- 20 microm longitudinally, +/- 0.036 degrees rotationally, and +/- 0.007degrees in tilt.

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PubMed2003

Determination of the optimum cluster parameters in a clustered free-space optical interconnect.

A model for a clustered free-space optical interconnect is developed and is used to determine the maximum array density that can be achieved, together with the optimal cluster parameters that maximize this density. This model includes misalignment tolerance and the impact of multimode vertical-cavity surface-emitting laser beams. We find that for short interconnect distances, the maximum channel density is limited by the speed of the relay lenses, but as the interconnect distance increases, geometric aberrations become the limiting factor. We also determine the interconnect distance below which a micro-channel relay is more suitable and the distance above which a single-lens solution is adequate.

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PubMed2003

Design, implementation, and characterization of a folded spot-array generator for a modulator-based free-space optical interconnect.

A folded structured light generator is presented. This spot generator is to be used in a modulator-based free-space optical interconnect. Three cascaded diffractive optical elements produce 4 x 8 clusters on an 800 microm x 1600 microm pitch, in which each cluster is a 4 x 4 array of 13.1-microm-radius spots on a 90-microm pitch. The folded configuration is more compact than an existing linear spot-array generator and replaces 14 optical surfaces with eight surfaces. Details of the optical design, sensitivity analysis, alignment techniques, assembly, and test results are presented.

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PubMed2003

Design and implementation of a modulator-based free-space optical backplane for multiprocessor applications.

Design and implementation of a free-space optical backplane for multiprocessor applications is presented. The system is designed to interconnect four multiprocessor nodes that communicate by using multiplexed 32-bit packets. Each multiprocessor node is electrically connected to an optoelectronic VLSI chip which implements the hyperplane interconnection architecture. The chips each contain 256 optical transmitters (implemented as dual-rail multiple quantum-well modulators) and 256 optical receivers. A rigid free-space microoptical interconnection system that interconnects the transceiver chips in a 512-channel unidirectional ring is implemented. Full design, implementation, and operational details are provided.

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PubMed2003

In situ technique for measuring the orthogonality of a plane wave to a substrate.

A new compact in situ method of measuring the perpendicularity of a plane wave to a substrate is proposed. Off-axis cylindrical Fresnel lenses are used to focus a portion of the incident plane wave onto target lines. The displacement of the focal line from the targets is determined by the degree of angular misalignment. The proposed design has been incorporated into a 10-mm-thick fused-silica module, which enables us to obtain an alignment precision of better than 0.0083 degrees. This method is designed for use in optical assembly procedures that require an incident collimated beam that is normal to the alignment features. Experimental results are presented.

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PubMed2002

512-channel vertical-cavity surface-emitting laser based free-space optical link.

A vertical-cavity surface-emitting laser based bidirectional free-space optical interconnect has been implemented to interconnect two printed circuit boards. A total of 512 clustered channels with a density of 2844 channels/cm2 are transmitted over a distance of 83 mm. The optical interconnect is a combination of refractive microlenses and diffractive minilens relays.

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PubMed2002

Implementation of a compact, four-stage, scalable optical interconnect for photonic backplane applications.

We report on the implementation of a dense 512-beam free-space optical interconnect linking four optoelectronic VLSI chips at the backplane level. The system presented maximizes the positioning tolerances of the components by use of slow f-number (f/16) Gaussian beams and oversized apertures. A beam-clustering scheme whereby a 4 x 4 array of beams is transmitted by each minilens is used to provide a high channel density. A modular approach is used to decrease the number of degrees of freedom in the system and achieve passive alignment of the modules in the final integration phase. A design overview as well as assembly and experimental results are presented.

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