System-level packaging is one of the critical issues that need to be addressed for free space optical interconnections (FSOI) to become useful in desktop systems. The performance of FSOI, e.g., in terms of system bit-error rate, is greatly affected by misalignments in the optical system. Therefore tolerancing, i.e., the ability to analyze and predict the effects of misalignments in the system, is of prime importance to system designers. We introduce an approach in which we study the effects of optical misalignments and other tolerance factors using statistical methods. We use Monte Carlo simulations, design of the experiments, and regression techniques to fit a polynomial equation that expresses the relationship between the system performance and the tolerance factors. This prediction model can be used for design, cost optimization, and quality control purposes. In addition, we perform a sensitivity analysis to determine those tolerance variables that have the greatest effect on system performance.

A photorefractive beamsplitter (PRBS) is introduced as an alternative to a polarizing beamsplitter (PBS) for coupling optical power into reflective modulators in a free-space optical interconnection (FSOI) system. The PRBS uses a single difulaction grating recorded in a photorefractive material to redirect the incident laser light into the first diffraction order and onto the modulators. Reflected interconnection light not matching the Bragg angle criteria transmits through the beamsplitter uncoupled. Experimental results show that the PRBS provides better uniform transmission for off-axis beams than the currently used PBS.Keywords: photorefractive, beamsplitter, free space optical interconnect systems 1. TECHNICAL RATIONALE FOR PRBS Free space optical interconnection systems provide a compact and efficient means of communication in massively parallel computer systems. Free space optical interconnection systems utilizing reflective modulators as transmitters require an optical device which can couple optical energy from a transverse direction into the modulators. As seen in Figure 1, this same device also needs to allow the optical beams reflected from the modulators to transmit through to the detectors on the opposite side. Therefore, this device needs to be highly efficient in redirecting light into the modulators as well as highly transparent to the interconnect light coming from the modulators. Optical power coupling device 0 0 7 Modulator Interconnection Detector plane beams plane Figure 1General system schematic for a free space optical interconnect system using reflection type modulators.In the FSOI system considered in this paper, as well as many existing or proposed systems, the interconnect paths will have many different angles. For example, corner modulators in the input plane could be connected to diagonally opposed SPIE Vol. 3010 • 0277-786X/971$l 0.00 207 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/17/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx detectors while center modulators could connect straight across to center detectors. Therefore the optical power coupling device must provide uniform transmission for a wide angular spectrum. Currently, the PBS is the device of choice in most modulator based FSOI systems. A PBS has a high reflectivity for the s polarization and a high transparency for p polarization. Due to the dielectric characteristics ofthe thin film coating in a PBS, the transmission efficiency varies with the incident angle. For example, if incident light with p polarization is 5 degrees off-axis, the transmission drops 20%'.Specifically, for the Optical Transpose Interconnect System, that has been shown to be useful for a large variety 1 algorithms on FSOI2'3'4, the f# requirement to maintain better than 95% transmission uniformity can be calculated through the following equation:5 l TiM and N represent the number of transmitters and receivers and 0 is the maximum acceptance angle. For a system of 4096 channels using a PBS, where MN64 and 0 ...

Derivatization is used to increase both negative-ion sensitivity and positive-ion sequence information in the liquid secondary-ion mass spectra (LSIMS) of a series of peptides. The derivatization method involves acylation with pentafluorobenzoyl fluoride in a single-step reaction, and the reaction mixture is applied directly to the probe tip for analysis. Acylation takes place at the unprotected N-terminus, tyrosine, and lysine. The derivatives exhibit increased signal-to-noise ratio for [M-H]- ions, especially where there is not already an acidic amino acid residue in the peptide. In positive-ion LSIMS, the N-terminal group acts to retain the charge at the N-terminus, simplifying the fragmentation by producing N-terminal fragment ions. It also increases positive-ion fragmentation, sometimes very dramatically, making sequence determination more straightforward. The simplicity of the process, together with the enhancements it provides, make this a generally useful method for obtaining peptide structural information.

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