Optical membrane technology for deep space optical communications filters

Large filters are being considered to allow large Earth-based optical communication receiver apertures to maintain communication with deep-space terminals as their orbits take them around the Sun. Optical membranes have been investigated as a promising substrate for such filters; their low weight offers great flexibility in mounting, while their ~10 micron thickness should be helpful in avoiding optical aberrations. Critical performance parameters of membrane filter samples are presented. Interferometry has shown generally good performance of the material for transmission applications, though aberrations near membrane seams are currently excessive. Scattering measurements at 1.064 microns show scatter of .05-.15 sr^-1, though variations of the plastic formulation show promise for reducing this to .01 sr^-1 . Finally, in-situ application of filter samples have demonstrated that their insertion currently results in an increase to stellar point spread functions of ~3-4 arcseconds at the intended 1.064 micron transmission wavelength. Filter designs concentrating on metallic induced-transmission filters are presented for application as a solar rejection filter on membrane substrates. Accomplishing efficient rejection of solar radiation, and high throughput at the communication wavelength with relatively few layers, these filter designs appear ideal for application to large filters for earth-based optical communication receivers