Title Slide

State-of-the-art tools for next-generation underwater optical imaging systems1Linda Mullena, Shawn OConnora, Brandon Cochenoura, Fraser Dalgleishb a Naval Air Systems Command, NAVAIR, Electro-Optics and Special Mission Sensors Division, 22347 Cedar Point Road, Patuxent River, MD 20670;b Harbor Branch Oceanographic Institute, Ocean Visibility and Optics Lab, Fort Pierce, FL 34946.For Official Use Only - Unclassified

Application: Underwater optical imaging Paper 8724-1 2NonscatteredForward-scatteredBackscatteredReceiverdTRdTO = dRO >> dTRLaser

Above-water

Underwater

Backscatter

Forward-scatter=+AmplitudetimeAmplitudetimeAmplitudetimeBandpassFiltered*Need a way to discriminate against backscattered and forward-scattered light*New approach modulated pulsePaper 8724-1 3U. S. Patent No. 5,822,047, 13 October, 1998.Macro pulse (pulse envelope):Coarse target rangingEnables receiver to be operated in gated modeMicro pulses (modulation):Backscatter/forward scatter suppressionFine target rangingNonscatteredForward-scatteredBackscatteredReceiverdTRdTO = dRO >> dTRLaser

Discussion frequency spectrumPaper 8724-1 4frequency100MHz1000MHzBackscatterForward scatterSolar ambientShot noiseBy modulating light and AC coupling receiver :Shift operating point away from these low frequency signalsOptimize A/D dynamic rangeHowever, optical receiver still sees these signals consumes optical dynamic range, generates shot noiseModulated pulsereturnNon-modulatedpulse returnFor DC-coupled receiver low frequency signals can limit performanceState-of-the-art toolsPaper 8724-1 5Modulated Pulse Source: Navy SBIR Topic N07-036 Modulated Pulsed Laser Sources for Imaging Lidars 3 Phase II projects Fibertek, SA Photonics MOPA configuration (low energy, high rep rate)AdvR electro-optic beam deflector modulator (high energy, low rep rate applications)SPAWAR Phase II.5 for Fibertek source for dual use (comms/imaging)Modulated Pulse Receiver: Navy SBIR Topic N08-032 Hybrid lidar-radar receiver for underwater imaging applications 2 Phase II projects SA Photonics and ATGHigh speed, high sensitivity, large area photodetector and radar processingModulated Pulse performance prediction model developed by Dr. Eleonora Zege (National Academy of Sciences, Belarus)Modulated pulse receiverPaper 8724-1 6Objective of SBIR Phase II: develop photoreceivers with high speed (GHz), large aperture (>1cm), and high sensitivity (gain >1000) that can also be gated quickly (ns) Photonis 5 stage Photomultiplier tube (PMT):Bandwidth: 1GHzAperture: 12mm diameterGain: 10000Gate rise time: 50nsGate extinction: 10dB Average photocurrent: 15dB Average photocurrent: