Final Activity Report Summary - UFOS (Integrated Ultrafast Optical Pulse Processors)
The fellow's scientific activity has explored two distinct themes of research: (i) the investigation of integrated optical devices for photonic applications and (ii) the development and exploitation of a high-intensity terahertz source.
Regarding the first topic, a photonic temporal integrator has been developed, i.e. a device capable of performing the time integral of an arbitrary optical input. As expected for an all-optical technology, a photonic integrator can provide processing speeds orders of magnitude larger than its electronic counterpart. Another striking feature is that it enables the processing of complex information, whereas an electronic integrator is restricted to processing real data. The integrator has been used to implement an integrated pulse-shaper (which was the primary objective of the proposed project) capable of delivering flat-top waveforms by integrating two consecutive and identical out-of-phase pulses. The time duration of the generated flat-top has been proven to be tuneable, by simply varying the delay between the two pulses.
Besides this, another integrated photonic device has been developed and characterised, namely a multiple wavelength source. Based on a doped-silca glass micro-ring resonator, the device possesses a low threshold power and its frequency spacing can be varied from few hundreds of gigahertz up to several terahertz. Its low loss, design flexibility, and CMOS compatibility may enable its use for telecommunications, computing, sensing, metrology and other areas.
As far as the second topic of research is concerned, the fellow contributed in developing the most intense terahertz source based on optical rectification in Zinc Telluride. Few-cycle terahertz pulses with microjoule-level energy have been obtained and this has enabled the implementation of some of the first nonlinear experiments at terahertz frequencies in direct band-gap semiconductors. Techniques as Z-Scan, terahertz-pump / terahertz-probe and optical-pump / terahertz-probe have been employed to explore the nonlinear dynamics of free-carriers in both n-doped and photoexcited samples. The mechanism that dominates this kind of interactions have been found to be intervalley scattering and a simple two-valley electron transfer dynamic model coupled with a standard Drude-like response of free carriers in semiconductors well explains the experimental results.
Regarding the first topic, a photonic temporal integrator has been developed, i.e. a device capable of performing the time integral of an arbitrary optical input. As expected for an all-optical technology, a photonic integrator can provide processing speeds orders of magnitude larger than its electronic counterpart. Another striking feature is that it enables the processing of complex information, whereas an electronic integrator is restricted to processing real data. The integrator has been used to implement an integrated pulse-shaper (which was the primary objective of the proposed project) capable of delivering flat-top waveforms by integrating two consecutive and identical out-of-phase pulses. The time duration of the generated flat-top has been proven to be tuneable, by simply varying the delay between the two pulses.
Besides this, another integrated photonic device has been developed and characterised, namely a multiple wavelength source. Based on a doped-silca glass micro-ring resonator, the device possesses a low threshold power and its frequency spacing can be varied from few hundreds of gigahertz up to several terahertz. Its low loss, design flexibility, and CMOS compatibility may enable its use for telecommunications, computing, sensing, metrology and other areas.
As far as the second topic of research is concerned, the fellow contributed in developing the most intense terahertz source based on optical rectification in Zinc Telluride. Few-cycle terahertz pulses with microjoule-level energy have been obtained and this has enabled the implementation of some of the first nonlinear experiments at terahertz frequencies in direct band-gap semiconductors. Techniques as Z-Scan, terahertz-pump / terahertz-probe and optical-pump / terahertz-probe have been employed to explore the nonlinear dynamics of free-carriers in both n-doped and photoexcited samples. The mechanism that dominates this kind of interactions have been found to be intervalley scattering and a simple two-valley electron transfer dynamic model coupled with a standard Drude-like response of free carriers in semiconductors well explains the experimental results.