Ultra-wideband radio frequency signal analysis using spatial-spectral holography
Thursday, November 11, 2010 – 2:45pm
Dr. Kristian D. Merkel
I will cover the basics of the interaction of coherent light with cryogenically cooled crystal absorbers and how this science has evolved to provide a basis for an emerging technology known as spatial-spectral holography. I will also discuss my personal observations on academia and compare doing R&D in an academic setting to doing R&D, primarily funded by the Small Business Innovative Research (SBIR) program, in a commercial small business.
The core technology has its roots in the coherent interaction of light with matter. Basic phenomena are described as photon echoes, spectral holeburning, andoptical coherent transients, among others. A basic primer of the field is Optical Resonance and Two-Level Atoms, by L. Allen and J.H. Eberly (Wiley, 1975)
A desirable material should exhibit absorption of the light by a two level transition with a wide absorption band comprised of narrow atomic resonances. Materials typically used for absorption of light are rare earth doped crystals, such as Thulium or Erbium doped into YSO, YAG, or LiNbO3, which require cryogenic cooling to achieve narrow frequency resolution. Typical values in Tm:YAG are 20 GHz absorption bandwidth, 20 kHz frequency resolution at 4K, and lifetimes of atoms in excited states of ~ 1ms.
The technical approach to an RF receiver is based on the phase sensitive recording of RF energy based on the conversion of RF energy to optical energy via an electro-optical phase modulator (EOPM) and subsequent irradiation of coherent modulated laser light onto the unique optical material, the so called spatial spectral (S2) holographic crystal. The S2 sensor operates by absorption and performing physical Fourier transforms, which can provide high image rates of 1000’s of frames per second, while providing over 20 GHz instantaneous bandwidth (IBW), and with ~100 kHz resolution bandwidth (RBW). S2 materials thus record the phase sensitive spectra of wideband RF signals, and provide real time, 100% time-continuous signal analysis over the full IBW at a fast update rate (UR) of up to 10,000 frames per second. Functions of spectral analysis, direction finding and correlative signal processing will be discussed.