Efficient Frequency Conversion and Optical Amplification to Improve Detection of Chemical and Biological Agents

There is a need to improve the sensitivity of chemical and biological sensing LIDAR systems so that standoff distances can be increased. LIDAR sensing systems have to cover ranges of 50 m to 20 km. However, their sensitivity is limited by the need to keep the laser transmitter power below the eye-safe limit. We propose to use Periodically-Poled Stoichiometric Lithium Niobate (PPLN) for improved frequency conversion efficiency in shifting received 3 to 5 micron mid-wave band LIDAR signals to the 1.5 micron optical telecommunications band. At 1.5 microns, commercial fiber optic amplifiers and detectors may be conveniently employed to ensure shot-noise limited detection and significantly improved signal-to-noise ratio. The optical gain stages may be based on Erbium Doped Fiber Amplifier or Raman Fiber Amplifier technologies. Such amplifiers are capable of producing gains of more than 40 dB with Noise Figures of less than 6 dB. The combination of the new tunable frequency conversion device with optical amplification and other system improvements will result in greater than 20 dB improvement in signal-to-noise ratio and will, therefore, triple the standoff measurement distance, reduce signal processing time, and offer greater frequency agility.