This paper covers the performance of a high speed analogue data transmission system. This system uses multiple Mach-
Zehnder optical modulators to transmit and record fusion burn history data for the Gas Cherenkov Detector (GCD) on
the National Ignition Facility. The GCD is designed to measure the burn duration of high energy gamma rays generated
by Deuterium-Tritium (DT) interactions in the NIF. The burn duration of DT fusion can be as short as 10ps and the
optical photons generated in the gas Cherenkov cell are measured using a vacuum photodiode with a FWHM of ~55ps.
A recording system with a 3dB bandwidth of ≥10GHz and a signal to noise ratio of ≥5 for photodiode output voltage of
50mV is presented. The data transmission system uses two or three Mach-Zehnder modulators and an RF amplifier to
transmit data optically. This signal is received and recorded by optical to electrical converts and a high speed digital
oscilloscope placed outside of the NIF Target Bay. Electrical performance metrics covered include signal to noise ratio
(SNR), signal to peak to peak noise ratio, single shot dynamic range, shot to shot dynamic range, system bandwidth,
scattering parameters, are shown. Design considerations such as self-test capabilities, the NIF radiation environment,
upgrade compatibility, Mach-Zehnder (MZ) biasing, maintainability, and operating considerations for the use of MZs are
covered. This data recording system will be used for the future upgrade of the GCD to be used with a Pulse Dilation
PMT, currently under development.
|