Andrea Bahgat Shehata

Telecommunications-band heralded single photons from a silicon nanophotonic chip

A highly nonlinear (γ≈3700/W·m) silicon coupled-resonator-optical-waveguide generated heralded single photons (g⁽²⁾ (0) ≤ 0.19 ±0.03) and widely-spaced photon pairs with coincidences-to-accidentals ratio >;10 (cw) and >;23 (pulsed), and outperformed a 54× longer silicon nanophotonic waveguide.

Fully programmable single-photon detection module for InGaAs/InP single-photon avalanche diodes with clean and sub-nanosecond gating transitions

We present the design and characterization of a modern near-infrared photon counting module, able to exploit the best performance of InGaAs/InP single-photon avalanche diodes for the detection of fast and faint optical signals up to 1.7 μm. Such instrument is suitable for many applications, thanks to the user-friendly interface and the fully adjustable settings of all operating parameters. We extensively characterized both the electronics and the detector, and we validated such instrument up to 133 MHz gate repetition frequency, for photon-counting and photon-timing applications, with very clean temporal response and excellent timing performance of less than 100 ps.

Time-resolved diffuse optical spectroscopy up to 1700 nm by means of a time-gated InGaAs/InP single-photon avalanche diode.

We present a new compact system for time-domain diffuse optical spectroscopy of highly scattering media operating in the wavelength range from 1100 nm to 1700 nm. So far, this technique has been exploited mostly up to 1100 nm: we extended the spectral range by means of a pulsed supercontinuum light source at a high repetition rate, a prism to spectrally disperse the radiation, and a time-gated InGaAs/InP single-photon avalanche diode working up to 1700 nm. A time-correlated single-photon counting board was used as processing electronics. The system is characterized by linear behavior up to absorption values of about 3.4 cm−1 where the relative error is 17%. A first measurement performed on lipids is presented: the absorption spectrum shows three major peaks at 1200 nm, 1400 nm, and 1700 nm.

Time-domain diffuse optical spectroscopy up to 1700 nm using an InGaAs/InP Single-Photon Avalanche Diode

Time domain diffuse optical spectroscopy provides the absorption and scattering properties of biological tissues and diffusive materials. Few measurements are available at discrete wavelengths beyond 1100 nm, and just one time-domain system continuously tuneable up to 1400 nm. We developed a time-domain system, based on a continuously tuneable supercontinuum pulsed source, and a custom InGaAs/InP Single-Photon Avalanche Diode. Operation was demonstrated in the 1100-1700 nm range with a spectral resolution of 15 nm, a temporal resolution of 150 ps and a background of 6000 counts/s. A first example of application on the optical characterization of collagen powder is given.

InGaAs/InP SPAD photon-counting module with auto-calibrated gate-width generation and remote control

We present a photon-counting module based on InGaAs/InP SPAD (Single-Photon Avalanche Diode) for detecting single photons up to 1.7 μm. The module exploits a novel architecture for generating and calibrating the gate width, along with other functions (such as module supervision, counting and processing of detected photons, etc.). The gate width, i.e. the time interval when the SPAD is ON, is user-programmable in the range from 500 ps to 1.5 μs, by means of two different delay generation methods implemented with an FPGA (Field-Programmable Gate Array). In order to compensate chip-to-chip delay variation, an auto-calibration circuit picks out a combination of delays in order to match at best the selected gate width. The InGaAs/InP module accepts asynchronous and aperiodic signals and introduces very low timing jitter. Moreover the photon counting module provides other new features like a microprocessor for system supervision, a touch-screen for local user interface, and an Ethernet link for smart remote control. Thanks to the fullyprogrammable and configurable architecture, the overall instrument provides high system flexibility and can easily match all requirements set by many different applications requiring single photon-level sensitivity in the near infrared with very low photon timing jitter.

Heralded single photons from silicon coupled-resonator optical waveguides

We leverage the high spontaneous four-wave-mixing nonlinearity (γ≈4150/W·m) of silicon coupled-resonator optical waveguides to demonstrate a telecommunications-band, heralded single photon source. The generated light is antibunched with g⁽²⁾(0) ≈ 0.19 ±0.03 at low power.

Optical Spectroscopy up to 1700 nm: a Time-Resolved Approach Combined with an InGaAs/InP Single-Photon Avalanche Diode

Time-resolved spectroscopy has been exploited mostly up to 1100 nm: our system reaches up to 1700 nm, thanks to a supercontinuum laser source and an InGaAs/InP Single-Photon Avalanche Diode. A first in-vivo application is presented.

Photon counting module based on InGaAs/InP Single-Photon Avalanche Diodes for near-infrared counting up to 1.7 µm

InGaAs/InP Single-Photon Avalanche Diodes (SPADs) have good performance to be successfully employed in many applications that demand single photon detection in the 1 – 1.7 µm wavelength range. However, in order to fully exploit such detectors, they have to be operated in optimized working conditions using dedicated electronics. We present the design and experimental characterization of a high-performance compact detection module able to operate at best InGaAs/InP SPADs. The module includes a pulse generator for gating the detector, a front-end circuit for avalanche sensing, a fast circuitry for detector quenching and resetting and some sub-circuits for signal conditioning. Experimental measurements prove the state-of-the-art performance and its great flexibility to fit the different applications.