A wavelength-controlled continuous beam-steering four-element X-band (8- to 12-GHz) phased array antenna system is presented. The system is based on the continuously tunable optical true-time-delay technique. Dispersion-enhanced waveguide holograms were proposed and used to fabricate the optical true-time-delay devices. The devices are characterized both theoretically and experimentally. The wavelength of a laser was tuned within the system to get continuously tunable true time delay. The time delay was measured for a wavelength tuning range from 1537 to 1547 nm in 10-nm steps. The far-field radiation patterns of the antenna system were measured at 9 and 10.3 GHz, and they showed no beam squint. The true-time-delay formation idea presented here is suitable for not only X-band, but also for higher microwave frequencies, such as K-band.
Empirical data regarding the radiation induced responses of Mach Zehnder interferometric electro-optic polymer based modulators (PBMs) operating at 1310 and 1550 nm and broadband InP quantum dot (QD) polymer photodetectors (PPDs) operating into the near infrared (NIR) are reported. Modulators composed of spun-on materials and hybrid electostatically self assembled (ESA) and spun-on NLO materials are examined for changes to their half-wave voltage and insertion losses following a gamma-ray total dose of 163 krad(Si) and irradiation by 25.6 MeV protons at a fluence of ~10<sup>11</sup> cm<sup>-2</sup>. Pre- and post- irradiation responses of ESA grown polymer detectors using InP QDs are examined for photovoltage degradation and aging effects. The data indicates and excellent potential for developing polymer based photonic (PBP) devices with increased radiation resistance suitable for transition to photonic space applications.
Two second-order nonlinear optical chromophoric materials were investigated for their response to gamma-ray irradiations for doses ranging from approximately 10-104 krad(Si). Thin film polymer modulators composed of a mixture of amorphous polycarbonate and phenyltetraene [APC/CLD-1(CPW-1)] active regions with UV upper and lower UV claddings were investigated for their pre- and post-irradiation behavior. Modulator V<sub>π</sub> insertion loss, and extinction ratio responses were examined, while a blend of salmon deoxyribonucleic acid (DNA)- hexadeCetylTriMethylAmmonium Chloride (CTMA) film samples were studied for their spectral response following irradiations over the spectral range λ=240-2600 nm. Following irradiation ranging from 9.6-104 krad(Si), the DNA/CTMA films exhibited losses in transmissivity over the spectral range λ=882-2600 nm and increased transmissivity over portions of the 240 nm < λ < 882 nm band. Data from the study also suggested that strongly poled APC/CPW-1 modulators operating at λ=1550 nm and exhibiting low V<sub>π</sub> values were less likely to have their half-wave voltages affected by ionizing radiation. The optical insertion losses for the majority of the APC/CPW-1 irradiated mdolators were found to decrease following irradiation. Discussion of the experimental results and mechanisms believed responsible for the post-irradiation behavior and results are presented.
Future space-based platforms can and will benefit from the implementation of photonics in both analog and digital subsystems. This paper will discuss potential applications and advantages to the platforms through the use of photonics.
We study experimentally the photorefractive gratings decay in semi-insulating germanium doped cadmium telluride crystals. The estimates for the diffusion length of free carriers L<SUB>D</SUB> and for Debye screening length l<SUB>s</SUB>, for dark and photoconductivities of the sample are done from the angular and intensity dependences of the time constant.
Photorefractive ZnTe and CdTe crystals doped with vanadium and/or manganese were grown and characterized in the wavelength range of 0.63 micrometers to 1.52 micrometers . The highest gain was observed in ZnTe:Mn:V (1.5 cm<SUP>-1</SUP> at 0.63 micrometers ). Through the use of both dopants the effective trap density was increased over an order of magnitude to 4.8 X 10<SUP>15</SUP> cm<SUP>-3</SUP>. The wavelength sensitivity range of cadmium telluride photorefractives was extended to less than 0.6 micrometers in CD<SUB>0.55</SUB>Mn<SUB>0.45</SUB>Te:V.
A partially asymmetric quantum-well Fabry Perot uses unequal partial reflections from front and back interfaces and balances destructive interference upon reflection by relying on intrinsic absorption in the quantum wells. The antireflection condition produces large modulation contrast ratios for reflected beams, while the partial reflections simultaneously allow transmission through the device. When the device is operated as a holographic optical element by incorporating a photorefractive quantum well structure in the Fabry Perot, output diffraction efficiencies can approach 100%. These holographic devices are optically addressed and electrically switched. In this paper we present theoretical calculations of the properties of partially asymmetric Fabry-Perot quantum wells.
A compact optical image correlator using orthogonal, wavelength-multiplexed Fourier transform holograms recorded in a photorefractive crystal is demonstrated. Cross-correlation and autocorrelation measurements were obtained using randomly selected test image against the set of reference images stored in the orthogonal data storage volume hologram. Over 20 holograms were recorded in the 645- to 651-nm wavelength range with >2% autocorrelation efficiency and 3-angstrom wavelength separation. A low-power tunable external cavity semiconductor laser was used for readout, further demonstrating the portability of this approach. The translation invariance of the input images was also investigated.
Optical switching properties of a photorefractive BaTiO3 crystal are studied. The data
shows a small but symmetric switching for ordinary polarized input beams and a larger but
nonsymmetric switching for extraordinary polarized beams. Slow drifts were also observed in the
outputs after switching with extraordinary beams. The extreme nonsymmetry and drifts are
believed to be caused by coupling that is due to gratings produced by internal reflections. We
suggest that these effects may make the photorefractive BaTiO3 crystal unsuitable for optical
switching applications but do not affect its ability to be used as a memory storage device with