We report the method of accurate diffraction efficiency control for multiplexed volume holographic gratings in dry photopolymer films (DuPont HRF-600). Based on the experimental evaluations of the grating formation characteristics in dry photopolymer films, we present the way to develop the practical recording schedules for the fabrication of holographic gratings under accurate diffraction efficiency control. Using this method, we obtained single holographic gratings with the desired diffraction efficiency (variation 2.5%) and high-efficiency equal-strength (47%/47%) double holographic gratings. As a practical application, we demonstrated the centralized optical backplane architecture with uniform fanouts using the single and equal-strength double holographic gratings we recorded.
A novel reconfigurable true-time delay feed for phased-array antennas working from X to Q (8-50GHz) frequency bands is presented. The reconfigurable optical true-time delay feed, employing monolithic integration of polymer waveguide delay lines and polymeric optical switches, has great advantages in providing power efficient, lightweight, and small size features. Optical switch technique provides large delay selections enabling the module to operate in ultra-broad radar bands. Polymer waveguides with optical propagation loss of less than 0.9dB/cm were achieved at 1550nm. 2X2 thermo-optic switchs as fast as 1ms were fabricated with an excess insertion loss of 0.5 dB in the "switching state" and 1.5dB in the "non-switching state". Reconfigurability of the true-time delay line was demonstrated through accurate time delay measurement.
Close-form expressions are used to analyze the spatial and angular linearity of the out-coupling volume holograms in wavelength division multiplexing/demultiplexing (WDM/WDDM). Optimal spatial linear out-coupling regimes are located. Some design criteria for volume holographic WDDM applicable to 800nm, 1300nm, and 1550nm optical wavelength window are addressed. As a design example, we deploy these criteria to design a passive surface normal input/output wavelength division demultiplexer (DMUX) working in the wavelength range of 768 ∼ 864nm. Coupling of the demultiplexed optical signal from the substrate modes to a linear multi-mode fiber array is verified with experiment. The importance of the spatial linearity of the out-coupling in volume holographic WDDM structure is highlighted and possible coupling of the signal to linear single-mode fiber array is mentioned.
The concept of a three-dimensionally interconnected optical backplane for a high-performance system containing multichip module boards, operating at 850 nm, is introduced. The backplane reported here employs 2-D vertical-cavity surface-emitting lasers (VCSELs) and photodetector arrays as transceivers. By integrating 250-m-pitch 2-D VC-SELs, microlenses, and photodetector arrays into our backplane design, we have demonstrated a multi-bus-line optical backplane and experimentally realized this architecture with 2-D VCSEL and detector arrays while using the third dimension as the signal-propagating direction. Such an approach greatly increases the aggregate bandwidth of the backplane. Packaging issues such as misalignment, cross talk, and signal-tonoise ratio are studied. Eye diagrams up to 1.5 GHz were obtained with clear eyes, and the frequency response of a single bus line shows a bandwidth of 2.5 THz.
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