Low-cost nanosecond electronic coincidence detector
  We present a simple and low-cost implementation of a fast electronic coincidence detector based on PECL logic with a TTL-compatible interface. The detector has negligible dead time and the coincidence window is adjustable with a minimum width of 1 ns. Coincidence measurements of two independent sources of Bose-Einstein distributed photocounts are presented using different coincidence window widths. 
Taehyun Kim, Marco Fiorentino, Pavel V. Gorelik, Franco N. C. Wong