John T. Shen

Translation-invariant object recognition system using an optical correlator and a super- parallel holographic random access memory

We demonstrate a translation-invariant VanderLugt correlator VLC for a set of images stored via holographic angle multiplexing of volume gratings in a polymeric substrate. The images read out from the volume gratings are optically correlated in a translation-invariant manner with a dc-suppressed holographic filter. The quality and efficiency of this correlator are observed to be nearly as good as that of another VLC with images directly from a spatial light modulator used as inputs. This ex- periment is the first step toward realizing a novel optical image recogni- tion system capable of identifying a query image through an exhaustive search in a large database of filter images stored in an ultrahigh capacity superparallel holographic random access memory SPHRAM. In this system, the identification of the query image is to be performed with a translation invariant, real-time VLC or a joint transform correlator JTC.

Shared-hardware alternating operation of a super-parallel holographic optical correlator and a super-parallel holographic random access memory

For practical pattern recognition and tracking systems, it is often useful to have a high-speed random access memory (RAM) that complements a holographic correlator. Recently, we have demonstrated a super-parallel holographic correlator, which uniquely identifies N im- ages from a database using only O(AN) number of detector elements. We show how this correlator architecture, operated in reverse, may be used to realize a super-parallel holographic random access memory. We present preliminary results, establishing the feasibility of the superparal- lel holographic random access memory, and show that essentially the same set of hardware can be operated either as the super-parallel holo- graphic optical correlator or as a super-parallel holographic random ac- cess memory, with minor reorientation of some of the elements in real time. This hybrid device thus eliminates the need for a separate random access memory for a holographic correlator-based target recognition and tracking system.

Shared-hardware alternating operation of a superparallel holographic optical correlator and a superparallel holographic RAM

For practical pattern recognition and tracking systems, it is often useful to have a high-speed random access memory (RAM), which complements a holographic correlator. Recently, we have demonstrated a super-parallel holographic optical correlator, which uniquely identifies N images from a database using only 2 number of detector elements. In this paper, we show how this correlator architecture, operated in reverse, may be used to realize a super-parallel holographic random access memory. We present preliminary results establishing the feasibility of the super-parallel holographic random access memory, and show that essentially the same set of hardware can be operated either as the super-parallel holographic optical correlator or as a super-parallel holographic random access memory, with a minor reorientation of some of the elements in real time. This hybrid device thus eliminates the need for a separate random access memory for a holographic correlator based target recognition and tracking system.

A simple method for Bragg diffraction in volume holographic gratings

We discuss a simple beam interference approximation method for deriving the angular selectivity of diffraction in weakly modulated volume holographic gratings. The results obtained using the multiple beam interference model agree qualitatively with the results obtained from a physical optics treatment of the coupled-wave theory for volume holographic gratings.

Demonstration of a spectrally multiplexed holographic stokesmeter

A holographic Stokesmeter utilizes polarization sensitivity of volume gratings to determine the Stokes parameters of an input beam. We demonstrate a spectrally multiplexed holographic stokesmeter for two different wavelengths of 532nm and 780nm simultaneously

Demonstration of a Multiwave Coherent Holographic Beam Combiner in a Polymeric Substrate

We demonstrate an efficient coherent holographic beam combiner using angle multiplexing of gratings. Our experimental results compare well with the theoretical model based on the coupled wave theory of multi-wave mixing in a passive medium.

Holographic Stokesmeter utilizing the polarization dependency of thick holographic substrates

Thick holographic gratings can be designed to have a strong polarization dependence of the diffraction efficiency. Such gratings can be used in a holographic Stokesmeter that can determine all four Stokes parameters in parallel. We demonstrate the theory of this holographic Stokesmeter and show preliminary results.

Spatio-angular parallelism in a holographic correlator and random access memory

The same elements of the architecture for a super-parallel holographic correlator can be operated as a holographic random access memory. This shared architecture allows the correlation or memory readout to occur in parallel at all spatial locations and at all angles.