Fapeng Yu

A real-time programmable joint transform correlator

Abstract A real-time programmable joint transform correlator (PJTC) utilizing a magneto-optic device (MOD) with a liquid crystal light value (LCLV) is presented. Object functions to be correlated are written into a light MOD with a programmable microcomputer, as input signals. Real-time correlation is taken place by a LCLV, as a square low detector, with a coherent read out. Cross correlation between the input functions can be obtained through the inverse Fourier transform of the read-out coherent illumination. A brief discussion of the proposed PJTC and a few experimental results are provided.

Implementation of a non-zero-order joint-transform correlator by use of phase-shifting techniques

The implementation of non-zero-order joint-transform correlators (JTCs) is presented. The zero-order spectra (i.e., the autocorrelation power spectra) are removed from the joint-transform power spectrum by use of phase-shifting techniques by which the output diffraction and input spatial domain can more efficiently be utilized. Applications of the phase-shifting techniques to both conventional JTCs and phase-transformed input JTCs (PJTCs) are discussed. Compared with the conventional JTC, the PJTC has the advantages of higher light efficiency, a better signal-to-clutter ratio, and the simplicity to realize phase shifting. We anticipate that the proposed non-zero-order JTCs should have a significant impact on the future development of more efficient JTCs.

Optical neural network with pocket-sized liquid-crystal televisions.

A compact optical neural network that uses high-resolution liquid-crystal televisions has been constructed. System design considerations and an experimental demonstration of the liquid-crystal television neural network are reported.

Investigation of Ca3TaGa3Si2O14 piezoelectric crystals for high temperature sensors

The dielectric and electromechanical properties of fully ordered Ca3TaGa3Si2O14 (CTGS) crystals were investigated over the temperature range of −60∼700 °C. The highest electromechanical coupling factor, k26 (18.9%) and piezoelectric coefficient, d26 (−11.5 pC/N) were obtained for (YXl)-25° cuts. The temperature dependent behavior of resonance frequency (fr) was investigated in single-rotated thickness shear mode (TSM) (YXl)θ cuts (θ = −35°∼10°). The turnover temperatures of resonance frequency were found to increase from 20 °C to 330 °C, as the rotation angle θ varied from −22.5° to −35°. Bulk acoustic wave (BAW) resonators based on Y(−30°) monolithic disks with a fundamental frequency ∼2.87 MHz were fabricated, where the in air mechanical quality factor Q was found to be on the order of 24000 and 10000 at 20 °C and 700 °C, respectively. The high coupling k26, high mechanical Q, and high electrical resistivity (16 MΩ·cm) at 700 °C, together with the near zero TCF characteristics at elevated temperatures, ...

Investigation of zero temperature compensated cuts in langasite-type piezocrystals for high temperature applications

Langasite-type crystals, including La3Ga5.5Nb0.5O14 (LGN), and La3Ga5.5Ta0.5O14(LGT) with disordered structure, and Ca3TaGa3Si2O14 (CTGS) and Ca3NbGa3Si2O14 (CNGS) with ordered structure, were grown using the Czochralski method. Resistivity was studied as a function of temperature. Temperature coefficients of frequency (TCFs) for different cuts were investigated in the above crystals at elevated temperatures, which were found to be ±11 ppm K−1 and ±6.0 ppm K−1 up to 400 °C for LGN (YXl)1.5° and LGT (YXl) − 20° cuts, respectively, in thickness shear mode, while the TCF was found to be 21 ppm K−1 up to 800 °C for CTGS (YXl) − 20° and CNGS (YXl) − 20°. Furthermore, the dielectric and electromechanical behaviour of the above crystals with low TCF cuts as a function of temperature were studied. It was observed that CTGS and CNGS crystals with an ordered structure possessed temperature independent dielectric and electromechanical behaviour up to 800 °C, making CTGS and CNGS potential candidates for high temperature sensor applications.

Color signal correlation detection by matched spatial filtering

A polychromatic correlation detection technique by complex spatial filtering is presented. This technique utilizes a diffraction grating and three co-lineared (red, green, and blue) coherent sources. The technique of complex spatial filter synthesis for the polychromatic corelation detection is demonstrated. This technique offers true color correlation detection which is very suitable for color signal recognition and identification. The correlation diffraction efficiency with this technique is generally higher than that of the wavelength-multiplexed technique. Several interesting experimental demonstrations of this color signal correlation detection scheme are provided. Finally we note that this color signal detection technique is a simple and versatile processing technique which has broad range of applications of complex color signal detection, recognition and identification.

Dielectric and electromechanical properties of rare earth calcium oxyborate piezoelectric crystals at high temperatures

The electrical resistivity, dielectric, and electromechanical properties of ReCa₄O(BO₃)₃ (ReCOB; Re = Er, Y, Gd, Sm, Nd, Pr, and La) piezoelectric crystals were investigated as a function of temperature up to 1000°C. Of the studied crystals, ErCOB and YCOB were found to possess extremely high resistivity (p): p >; 3 × 10⁷ ω.cm at 1000°C. The property variation in ReCOB crystals is discussed with respect to their disordered structure. The highest electromechanical coupling factor κ₂₆ and piezoelectric coefficient d₂₆ at 1000°C, were achieved in PrCOB crystals, with values being on the order of 24.7% and 13.1 pC/N, respectively. The high thermal stability of the electromechanical properties, with variation less than 25%, together with the low dielectric loss (<;46%) and high mechanical quality factor (>;1500) at elevated temperatures of 1000°C, make ErCOB, YCOB, and GdCOB crystals promising for ultrahigh temperature electromechanical applications.

Phase-encoded input joint transform correlator with improved pattern discriminability.

The concept of using phase-encoded input representation in a joint transform correlator is presented, in which we show that the phase-encoded input joint transform correlator is an optimal filtering system that improves detection efficiency and pattern discriminability.

Optical parallel logic gates using inexpensive liquid-crystal televisions.

The optical implementation of parallel logic gates using inexpensive liquid-crystal televisions (LCTVs) is demonstrated, and basic experimental results are presented. While it is certainly unreasonable to expect general-purpose optical computers to be built from LCTVs, demonstration-level systems can be built, from which a great deal may be learned.

Cross-talk noise in a wavelength-multiplexed reflection-type photorefractive fiber hologram

We have analyzed the cross-talk noise as affected by the wavelength spread that is due to the spectral width of the light source in a wavelength-multiplexed reflection-type photorefractive fiber hologram. The spectral bandwidth of each multiplexed channel limited by the cross-talk noise is discussed. The signal-to-noise (cross-talk) ratio is analyzed, whereby we have shown that this ratio is sensitive to the separation between adjacent multiplexed channels and to the spectral width of the light source. The cross-talk-limited storage capacity for practical photorefractive fibers is evaluated.