|Thesis abstract: |
The research activity was focused on the study, the design, the development and the characterization of innovative electronics for single-photon counting in the visible and near infrared range. In the last years, single photon detection became more and more important where very faint or ultra fast optical signals must be measured. Advanced applications can be found in many fields, such as measurement of fluorescent decays, characterization of new materials, VLSI testing, quantum physics, etc.
Different kinds of single-photon detectors have been developed in the past. Single photon avalanche diodes (SPADs) proved to have good performance in terms of photon detection efficiency and timing jitter. Silicon SPADs are sensitive up to 1100 nm, while InGaAs/InP SPADs can be employed to detect photons from 900 nm to 1700 nm.
A high-performance InGaAs/InP single-photon detection module has been developed. Through all steps of the design and development the goal was to offer high flexibility of the overall instrument, in order to be adapted to the different requirements of the near-infrared applications mentioned above. All main system parameters are configurable in a wide range. The wide-band front-end electronics allows for the fast gating of the detector and for the low time jitter avalanche sensing. An extensive experimental characterization proved performance superior with respect to other state of the art single photon detection modules. In particular an effective afterpulsing reduction was measured thanks to prompt quenching of the avalanche by acting both at the anode and cathode side of the SPAD. The developed photon counting module constitutes the enabling technology for several scientific applications.
Two novel gating schemes for the sinusoidal enabling at gigahertz of InGaAs/InP SPADs have been conceived and developed. A free-running equivalent mode is obtained by keeping the SPAD gate signal unlocked from the synchronization reference of the optical waveform to be reconstructed. We called this working mode ¿gate-free¿. An extensive experimental characterization has shown how the SPAD performance improves compared with a classical square-wave gating scheme, especially for non-periodic high-throughput applications. When employing a 25 µm diameter SPAD, the average photon detection efficiency at 1550 nm is 4 %, the afterpulsing probability with a 1.5 ns count-off time is of about 1 %, the timing resolution is 90 ps (FWHM) and the maximum count rate is 650 Mcount/s.
Finally a 32 channels single-photon counting module for time-resolved measurements from the near ultraviolet to the near infrared range has been developed. It is based on a linear array of silicon CMOS SPADs, monolithically integrated together with the quenching circuit. The experimental characterization showed timing resolution uniform for all the channels (~ 100 ps of FWHM). The photon detection efficiency is good over a wide wavelength range, and achieves about 50 % at ? = 450 nm. The extremely low dark count rate and afterpulsing probability represent are the strong point of this CMOS SPAD array. This linear CMOS SPAD array can pave the way to new applications where multi-channel acquisitions of fast and faint optical waveforms have to be acquired, such as time-resolved spectrometers, through a very compact detection head with single-photon sensitivity.