Single photon detection at telecom wavelengths is of importance in many industrial applications ranging from quantum
cryptography, quantum optics, optical time domain reflectometry, non-invasive testing of VLSI circuits, eye-safe
LIDAR to laser ranging. In practical applications, the combination of an InGaAs/InP APD with an appropriate
electronic circuit still stands as the best solution in comparison with emerging technologies such as superconducting
single photon detectors, MCP-PMTs for the near IR or up-conversion technique.
An ASIC dedicated to the operation of InGaAs/InP APDs in both gated mode and free-running mode is presented. The
1.6mm2 chip is fabricated in a CMOS technology. It combines a gate generator, a voltage limiter, a fast comparator, a
precise timing circuit for the gate signal processing and an output stage. A pulse amplitude of up to +7V can be
achieved, which allows the operation of commercially available APDs at a single photon detection probability larger
than 25% at 1.55&mgr;m. The avalanche quenching process is extremely fast, thus reducing the afterpulsing effects. The
packaging of the diode in close proximity with the quenching circuit enables high speed gating at frequencies larger
than 10MHz. The reduced connection lengths combined with impedance adaptation technique provide excellent gate
quality, free of oscillations or bumps. The excess bias voltage is thus constant over the gate width leading to a stable
single photon detection probability and timing resolution. The CMOS integration guarantees long-term stability,
reliability and compactness.