A ten-meter hexagonally segmented Cassegrain optical telescope is being considered at the Jet Propulsion Laboratory for use as a research and development facility for optical communications technology. The goal of the study is to demonstrate technology which can eventually be used to develop a network of such telescopes to continuously track and communicate with the spacecraft. Hence, the technology has to be economical enough to allow replication for a ground or space based network. As we need to collect signal photons only, the telescope cost can be substantially reduced by accepting lower image quality. An important design consideration for the telescope is its ability to look very close to the sun. The telescope for optical communications must function during the daytime. Indeed, for some planetary missions it may be necessary that the system be capable of looking within a few degrees of the sun. To enable this, a unique sunshade consisting of hexagonal tubes in precise alignment with the mirror segments has been proposed which will also serve as the support for the secondary. Recent progress on the design and analysis of such an optical reception station is discussed here. O-8194-0781-X1921$4.OO SPIE Vol. 1635 Free-Space Laser Communication Technologies IV(1992) / 109 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/25/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx [3] Mast, T., Nelson, J., and Welch, W, ' The effects of primary mirror segmentation on telescope image quality, ' Keck Observatory report no. 68, Oct.

This article describes optical subnets ofgrowzd based receiving stazionsfor earth-space optical communications. The optical subnet concepts presented here providefuilline-of-sight coverage ofthe ecliptic, 24 hours a day, with high weather availability. The technical characteristics ofthe optical station and the user terminal are presented as well as the effects ofcloud cover, transmittance through the atmosphere, and impact ofbackground noisefor day or night time operation upon the communication link. In addition, candidate geographic sites are identified, and a link designfor a hypothetical Pluto mission in 2015 is included.

Laser communication systems can be based on a wide range of wavelengths in the optical and infrared regimes. This article provides a rationale for the selection of wavelengths particularly suited for free space laser communication systems. The choice of wavelengths is based on an analysis of propagation issues, especially through the atmosphere, optical background noise, and the necessary technologies that include lasers, detectors, and spectral filters. The maturity of technology is assessed and given due consideration to identify suitable wavelengths for today's laser communication systems. Figures of merit are also developed where useful to provide a comparative estimate of expected system performance as afunction of wavelength.

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The ability of a real-time optical processor, using a computer-generated spatial frequency filter, to recognize any one of many different patterns often depends on the number of different reference patterns represented in the filter. An area multiplexing scheme has been devised that is similar to frequency-division multiplexing and is independent of amplitude or intensity superimposition. The increase in number of filter patterns at the expense of single pattern processing performance may make the scheme valuable for certain applications, especially phase-only processing. Results were compared with multiplexing schemes that distribute information about the reference patterns throughout the spatial frequency plane, but via superposition only or via entirely separate copies of the frequency distribution. Potential advantages of the area multiplexing scheme include an increased number of filter reference functions, less stringent transmittance linearity requirements for the CGH filter material, and the ability to incorporate different CGH carrier configurations. Disadvantages include reduced single-pattern processing performance, undesirable cross-modulation terms, and increased spatial resolution requirements in the filter.