The media position and tilt tolerances of a high numerical aperture (NA) holographic
data storage system are examined experimentally. The sources for these tolerances are explained
and techniques for optimizing the drive tolerances are described.
We propose performing ultrawideband RF spectrum analysis using spectral-hole-burning (SHB) crystals, which are crystal hosts lightly doped with rare earth ions such as Tm3+ or Er3+. Cooling SHB crystals to cryogenic temperatures suppresses phonon broadening, narrowing the ions' homogeneous linewidths to <100 kHz; local inhomogeneities in the crystal lattice shift the individual ionic resonances such that they're distributed over a bandwidth of 20 GHz or in some structurally disordered crystals to up to 200 GHz. Illuminating an SHB crystal with a beam modulated with multiple RF sidebands digs spectral holes in the crystal's absorption profile that persist for the excited state lifetime, about 10 ms. The spectral holes are a negative image of the modulated beam's spectrum. We can determine the location of these spectral holes by probing the crystal with a chirped laser and measuring the transmitted intensity. The transmitted intensity is the double-sideband spectrum of the original illumination blurred by a 100 kHz Lorentzian and mapped into a time-varying signal. Scaling the time series associated with the transmitted intensity by the instantaneous chirp rate yields the spectrum of the original illumination. Postprocessing algorithms undo distortion due to swept laser nonuniformities and ringing induced by fast chirp beams, eliminating the need for long dwell times to resolve narrow spectral features. Because the read and write processes occur simultaneously, SHB spectrum analyzers can operate with unity probability of intercept over a bandwidth limited only by the inhomogeneous linewidth. These capabilities make SHB spectrum analyzers attractive alternates to other approaches to wideband spectrum analysis.
Broadband RF imaging by spatial Fourier beam-forming suffers from beam-squint. The compensation of this frequency dependent beam-steering requires true-time-delay multiple beam-forming or frequency-channelized beam-forming, substantially increasing system complexity. Real-time imaging using a wide bandwidth antenna array with a large number of elements is inevitably corrupted by beam-squint and is well beyond the capability of current or projected digital approaches. In this paper, we introduce a novel microwave imaging technique by use of the spectral selectivity of inhomogeneously broadened absorber (IBA) materials, which have tens of GHz bandwidth and sub-MHz spectral resolution, allowing real-time, high resolution, beam-squint compensated, broadband RF imaging. Our imager uses a self-calibrated optical Fourier processor for beam-forming, which allows rapid imaging without massive parallel digitization or RF receivers, and generates a squinted broadband image. We correct for the beam squint by capturing independent images at each resolvable spectral frequency in a cryogenically-cooled IBA crystal and then using a chirped laser to sequentially read out each spectral image with a synchronously scanned zoom lens to compensate for the frequency dependent magnification of beam squint. Preliminary experimental results for a 1-D broadband microwave imager are presented.
We introduce a new approach to coherent LIDAR remote sensing by utilizing a quantum-optical, parallel sensor based on spatial-spectral holography (SSH) in a cryogenically cooled inhomogeneously-broadened absorber (IBA) crystal that is used to sense the LIDAR returns and perform the front-end range-correlation signal processing. This SSH sensor increases the LIDAR system sensitivity through range-correlation gain before detection. This approach permits the use of high-power, noisy, CW lasers as ranging waveforms in LIDAR systems instead of the highly stabilized, injection seeded and amplified pulsed laser sources required by most coherent LIDAR systems. The capabilities of the IBA media for many 10s of GHz bandwidth and sub-MHz resolution, while using either a coded waveform or just a high-power, noisy laser with a broad linewidth (e.g. a random noise LIDAR) may enable a new generation of improved LIDAR sensors and processors. Preliminary experimental demonstrations of LIDAR range detection and signal processing for random noise and chirped transmitted waveforms are presented.
We present an optical approach to 1-D broadband microwave imaging. The imager uses a Fourier optical beamformer to generate a squinted broadband image which is then spectrally resolved by burning a spatial distribution (an image) of spectral signals into a spectral-hole burning material. This spatial-spectral image corresponds to the spectral content of the image at each resolveable spatial point. These narrowband images may be sequentially read out with a chirped laser, scaled to compensate for beam squint, and summed to form a broadband microwave image.
We present a non-mechanical, dynamically programmable, all-optical image rotator, which can rotate an input image to any angle or a grid given by 360°/2n, where n is the number of stages. The image rotator uses cascaded stages in which each stage rotates the image by an angle given by half the previous stage. Each stage uses an Ferroelectric Liquid Crystal (FLC) polarization switch to select between a straight through path and a deflected path with an odd number of bounces, that when rotated to an angle, operates as an image rotating prism. An FLC is used for each stage to choose the polarization and therefore whether to rotate the image or not. By switching the FLC director orientation by 45 for each stage, images can be rotated to an arbitrary angle at a speed of several KHz.
We propose a novel, wideband spectrum analyzer based on spectral hole burning (SHB) technology. SHB crystals contain rare earth ions doped into a host lattice, and are cooled to cryogenic temperatures to allow sub-MHz hole burning linewidths. The signal spectrum is recorded in an SHB crystal by illuminating the crystal with an optical beam modulated by the RF signal of interest. The signal's spectral components excite those rare earth ions whose resonance frequencies coincide with the spectral component frequencies, engraving the RF spectrum into the crystal's absorption profile. Probing this altered absorption profile with a low power, chirped laser while measuring the transmitted intensity results in a time-domain readout of the accumulated RF signal spectrum. The resolution of the spectrum analyzer is limited only by the homogeneous linewidth of the rare earth ions (< 1 MHz when the SHB crystal is cooled to cryogenic temperatures). The spectrum analyzer bandwidth is limited by the inhomogeneous linewidth and by the electro-optic modulator bandwidth, both of which can be > 20 GHz.
We propose, analyze, and demonstrate the use of a holographic method for cohering the output of a fiber tapped-delay-line (FTDL). We perform a theoretical examination of the phase-cohering process and show experimental results for an RF spectrum analyzer based on a phase-cohered FTDL that shows 50 MHz resolution and bandwidths in excess of 2 GHz. Phase-cohering holography can operate on thousands of fibers in parallel, enabling both fiber tapped-delay-lines and the coherent fiber remoting of optically-modulated RF signals from antenna arrays.
We present a proof-of-concept optical experiment that demonstrates the
ability to record squinted broadband RF images formed by a Fourier beamforming phased-array antenna and subsequent squint correction using spatial spectral holography. A cryogenically cooled inhomogeneously broadened absorber (Tm3+:YAG) acts as a spectrally selective holographic medium which records the squinted RF image, covering a wide RF bandwidth (approaching 20 GHz) with resolution of approximately 1 MHz. Subsequently, a frequency-swept laser can read out the squinted image while a magnification-compensating motorized zoom lens synchronously corrects the magnification due to beam squint. Time-integration the image on a CCD detector array produces a squint-compensated broadband RF image, while detection with a MHz bandwidth detector can produce spectral estimates for all sources recorded with this imaging system.