A free space optical communication testbed using multi-channel optical code division multiplexing was demonstrated using a multiplexed optical transmitter utilizing SONET OC-12 signals, a pair of matched telescopes, and a single mode fiber coupled receiver and CDMA decoding system. An active beam alignment system was used at the receiver to maintain alignment on the receiver input fiber, with bit error rates under transmitter jitter of better than 2x10<SUP>-12</SUP> for a transmitter beam perturbation of 50 Hz and 45 (mu) rad peak to peak amplitude.
Ann add/drop multiplexer/demultiplexer using volumetric holographic crystal Bragg gratings and without use of circulators has been demonstrated. Multiplexed gratings with angle multiplexed reflection filters provide wavelength- selective reflection of one or more channels into or out of the fiber without disturbing the through channels. Overall channel add/drop losses of less than 3 dB and through channel losses of less than 0.5 dB have been demonstrated. Fabrication of holographic filters with the desired passband characteristics has also been demonstrated.
We present experimental results of holographic grating recording in the near ultra-violet (UV) in photorefractive LiNbO<SUB>3</SUB> crystals. The UV wavelength limits of Fe-doped LiNbO<SUB>3</SUB> crystals for UV grating filters have been established by characterizing the grating diffraction efficiency versus recording wavelength ranging from 300 to 400 nm. Methods for improving the UV performance of LiNbO<SUB>3</SUB> have also been investigated. It has been shown that the material absorption loss of Fe:LiNbO<SUB>3</SUB> crystals can be reduced and the grating efficiency can be a significantly improved by using proper post-grown oxidization treatment. Using the improved UV LiNbO<SUB>3</SUB> crystal, a sub-Angstrom bandwidth holographic grating imaging filter for solar observation at the Ca K-line (393.3 nm) has also been fabricated. Narrow bandwidth (22 pm, FWHM), large numerical aperture (f/15), large field-of-view (35 mrad), large aperture (15 mm in diameter) and high in-band diffraction efficiency (25%) have been successfully demonstrated. These results indicate an improved performance at a reduced cost as compared with currently available Lyot filters for solar magnetic field sensing at Ca K-line. Applications of the UV photorefractive holographic grating devices include solar and planetary observing, lidar receiving sub-systems for Earth remote sensing and atmospheric monitoring, and high density UV optical data storage.
Narrow bandwidth gratings, recorded using volume holography in photorefractive materials such as LiNbO<SUB>3</SUB>, have been demonstrated for use as filters, wavelength selective couplers, and optical data storage elements. Sub-angstrom bandwidths have been demonstrated in the visible and infrared. Reflectivities of up to 95% have been obtained. Applications in filtering, instrumentation, telecommunications, and optical storage are discussed.
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.