As the demand for multiple radio frequency carrier bands continues to grow in space
communication systems, the design of a cost-effective compact optical transmitter that
is capable of transmitting selective multiple RF bands is of great interest, particularly for
NASA Space Communications Network Programs. This paper presents experimental
results that demonstrate the feasibility of a concept based on an optical wavelength
division multiplexing (WDM) technique that enables multiple microwave bands with
different modulation formats and bandwidths to be combined and transmitted all in one
unit, resulting in many benefits to space communication systems including reduced
size, weight and complexity with corresponding savings in cost. Experimental results will
be presented including the individual received RF signal power spectra for the L, C, X,
Ku, Ka, and Q frequency bands, and measurements of the phase noise associated with
each RF frequency. Also to be presented is a swept RF frequency power spectrum
showing simultaneous multiple RF frequency bands transmission. The RF frequency
bands in this experiment are among those most commonly used in NASA space
Emerging technologies and continuing progress in research are making way for novel, high speed forms of optical data transfer. Vertical-cavity surface emitting laser (VCSEL) diodes operating at 1550nm have only recently become commercially available, while metal-semiconductor-metal (MSM) photodetectors are pushing the limits of contact lithography with interdigitated electrode widths reaching sub micron levels. We propose a novel, free-space optical interconnect operating up to 1Gbit/s utilizing commercially available 1550nm VCSEL diodes and newly fabricated InGaAs MSM photodetectors with functionality for both chip level and board level applications. We report on development, progress, and current work. Analyses of the divergent behavior and of the normalized frequency response of VERTILAS GmbH 1550nm VCSEL diodes for coupling to MSM photodetectors with a 50μm by 50μm active area are presented. The MSM photodetectors are fabricated on a pseudomorphic In<sub>0.9</sub>Ga<sub>0.1</sub>P-InP-InGaAs heterostructure and have gold interdigitated Shottky contacts with varying electrode width and spacing on the order of 1 to 3 microns. We discuss the calculated response of these MSM photodetectors as well as the fabrication and characterization of the devices. A report on bit error rate (BER) characteristics of the VCSEL diodes coupled to commercially available high-speed photodetectors and successively coupled to the novel MSM photodetectors integrated with commercially available transimpedance amplifiers (TIA) follows. The work accounted here will lead to the formation and characterization of a fully integrated 1Gbit/s free-space optical interconnect applying VCSEL diodes and MSM photodetectors operating at 1550nm for RF/microwave digital systems.
The design, fabrication and testing of a conformal K-Band circular array is presented. The array consists of sixteen linearly tapered slot antennas (LTSA). It is fed by a 1:16 microstrip line power splitter via electromagnetic coupling. The array has an omni- directional pattern in the azimuth plane. In the elevation plane the beam is displaced above the horizon.