Electromagnetic Launch Optical Telemetry Feasibility Study

Results of a preliminary study to evaluate the feasibility of optical telemetry on an EM launched projectile are discussed. At issue are the relative intensities of the optical noise received in the MCL catch tank from the muzzle flash versus the narrowband optical signal levels generated from tiny emitters onboard a projectile after being launched in the MCL. Two narrowband optical signal emitters are compared with the muzzle flash: a high intensity light emitting diode (AND190HAP LED) and a vertical cavity surface emitting laser (VCSEL). Optically filtered photo-detector responses of the broadband muzzle flash received in the catch tank after launch were spectrally analyzed in this work. The muzzle flash levels in 10-nm bands were observed to have effective intensities: ~1.1 mW·m centered at 610 nm and ~1.0 mW·m centered at 840 nm. The optical noise of the muzzle flash was found to overwhelm the received optical signal of the 612-nm LED by a factor of 20—indicating such a device will be unfeasible. On the other hand, the 0.86-mW·m effective intensity of a single 850-nm VCSEL—packaged with a domed-lens in a TO-46—was about the same as the muzzle flash. The lowfrequency spectral content of the optically filtered muzzle flash and the narrow optical beam of the VCSEL indicate several tens of dB improvement in S/N will likely be gained by telemetering information at frequencies of 5001000 MHz with a single VCSEL. Advantages of the VCSEL over the LED— significant improvements in: luminosity, optical bandwidth, modulation bandwidth, physical size, and power dissipation—suggest that such a device will prove feasible as an optical source on an EM launched projectile used for telemetry. It is recommended that these potential advantages be investigated next under high-g EM launch conditions using an array of VCSELs as an optical source to digitally telemeter frequency modulated information in the UHF band.