J. T. Shen

Coherent and incoherent beam combination using thick holographic substrates

We present a mathematical model of coherent and incoherent beam combination in a thick hologram. We also derive the formulae relating the read and write angles to the read and write wavelengths for the combiner. Furthermore, we present a new technique for determining the M#, and establish that the M# required for a coherent combiner is substantially less than that needed for an incoherent one.

Superparallel holographic correlator for ultrafast database searches

We describe a superparallel holographic optical correlator that performs two-dimensional spatial and angular multiplexing simultaneously. The key step in this architecture is the use of a holographic multiplexer to split a query image into many copies before it applies them to the holographic database. A holographic demultiplexer, in conjunction with an aperture, is used to identify the location and the angle of the brightest correlation peak. This architecture uses only O(square root of N) detector elements to search through N unsorted images in a single query. We demonstrate the basic features of this architecture, using three spatial locations with eight angle-multiplexed images in each location.

Shift-invariant real-time edge-enhanced VanderLugt correlator using video-rate compatible photorefractive polymer.

We demonstrated a real-time shift-invariant VanderLugt correlator (VLC). The VLC was implemented with a 37 μm thick bis-triarylamine side-chain polymer matrix photorefractive (PR) polymer composite operating at 532 nm wavelength. Correlation selectivity was enhanced by real-time edge enhancement. The advantage of the VLC is that its architecture allows overcoming the PR material response speed. A correlator of this type enables a fast shift-invariant search of a large optical image database. A high degree of shift invariance in our correlator was possible because of the material thickness. The angular bandwidth of this material was measured experimentally in a degenerate four-wave mixing setup, and it was found to be in a very good agreement with the theory.

Demonstration of a single exposure technique for determining the M/# of a holographic substrate

We propose and demonstrate a simple technique to determine the M/# for a holographic material. Using divergent object and reference beams, we write a single grating in the material. The resulting diffraction pattern can be analyzed to find the M/#

Ultrafast holographic Stokesmeter for polarization imaging in real time

We propose an ultrafast holographic Stokesmeter using a volume holographic substrate with two sets of two orthogonal gratings to identify all four Stokes parameters of the input beam. We derive the Mueller matrix of the proposed architecture and determine the constraints necessary for reconstructing the complete Stokes vector. The speed of this device is determined primarily by the channel spectral bandwidth (typically 100 GHz), corresponding to a few picoseconds.

Demonstration of a multiwave coherent holographic beam combiner in a polymeric substrate

We demonstrate an efficient coherent holographic beam combiner (CHBC) that uses angle multiplexing of gratings in a thick polymeric substrate. Our experimental results compare well with the theoretical model based on the coupled-wave theory of multiwave mixing in a passive medium. A CHBC of this type may prove useful in producing a high-power laser by combining amplified beams produced by splitting a master oscillator. Furthermore, the ability to angle multiplex a large number of beams enables a CHBC to be used in multiple-beam interferometry applications as a high-precision surface sensor.

Shift-invariant real-time edge-enhanced VanderLugt correlator using video-rate compatible photorefractive polymer

We show results from a real-time shift-invariant VandeLugt correlator in a new photorefractive polymer material. The thickness of the material allowed for fast shift-invariant search of a volume holographic database.

Demonstration of a thick holographic Stokesmeter

Using two sets of multiplexed thick-holographic gratings, we measured the Stokes parameters for three different polarization states of an input beam. These values compared well to values measured using the conventional quarter-wave plate/linear polarizer method.