Integrated Optical Mono-pulse Tracking System for Full Duplex Optical Communication
Conventional technology relies on a lens or array of lenses to cause incident energy to be aligned with the central detector. Tracking detectors are arranged around a central detector in close proximity and only receive energy as a result of misalignment. This misalignment causes a decrease in the energy incident on the main channel. Current technology does not allow for the use of multiple detecting elements of different frequencies in the main channel due to the non-wavelength dependent nature of the lenses. Current technology also does not allow for commingling of emitters and detectors in the region of the main channel due to the single point of focus produced by the lens.
The Johns Hopkins University Applied Physics Laboratory is developing an emitter/detector array and holographic beam splitter/combiner based on an integrated array of five or more photo-diodes and associated support components sufficient to allow demodulation and generation of a signal level voltage for each channel. The photo-diodes would be arranged in a square or diamond configuration with a photo-diode at each apex (tracking channels) and one or more at the center (primary or main channel), all deposited in close proximity on a single substrate. A key feature of this arrangement is the use of a holographic beam splitter that would allow substantial flexibility in the detector geometry. One possibility would be the interspersing of laser diodes among photo-detector diodes in the central position. By careful design of the holographic beam splitter to function as a combiner for the laser diodes and a splitter for the photo diodes, a full duplex system could be arranged. Further, the inherent wavelength sensitivity of the holographic splitter/combiner would allow the use of various optical frequencies on a single communications link. Neither of these capabilities would be possible using conventional technology of lenses and mirrors. Also, since the error channels receive energy at all times, and may be separated by a relatively large angle from the main channel detector, the system is much more sensitive to minor misalignments. This increased sensitivity allows corrections to be made without significant loss of signal on the main channel.
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