home » libere » 9. optical passive devices and terahertz frequencies 9. Optical passive devices and Terahertz frequencies
Contact person:
Miriam Vitiello
1. Graphene saturable absorbers. Saturable absorbers (SA) operating at terahertz (THz) frequencies can open new frontiers in the development of passively mode-locked THz micro-sources. We developed THz SAs by transfer coating and inkjet printing single and few-layer graphene films prepared by liquid phase exfoliation of graphite. Open-aperture z-scan measurements with a 3.5 THz quantum cascade laser show a transparency modulation ∼80%, almost one order of magnitude larger than that reported to date at THz frequencies.
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(a) z-scan normalized transmittance of a water-based graphenesaturable absorber probed with a 3.4 THz QCL; (b) Transmission electron microscopy images of few-layer graphene flakes from water based inks.
References:
V. Bianchi, T. Carey, L. Viti, L. Li, E.H. Linfield, A.G. Davies, A. Tredicucci, D. Yoon, P.G. Karagiannidis, L. Lombardi, F. Tomarchio, A. C. Ferrari, F. Torrisi, M.S. Vitiello, Terahertz saturable absorbers from liquid phase exfoliation of graphite, Nature Communications, 8, 15763 (2017).
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2. Intersubband polariton based saturable absorbers Intersubband (ISB) transitions in semiconductor multi-quantum well (MQW) structures are promising candidates for the development of saturable absorbers at terahertz (THz) frequencies. We developed polaritonic saturable absorbers at THz frequencies and exploit amplitude and phase-resolved two-dimensional (2D) THz spectroscopy on the sub-cycle time scale, to observe directly the saturation dynamics and coherent control of ISB transitions in a metal-insulator MQW structure.
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(a) Schematic diagram of the THz saturable absorber structure (b) Experimental principle showing the two identical THz pulses with fields εA and εB and delayed by a time τ, which prepare and interrogate the structure’s nonlinear response εAB.
References:
J. Raab, C. Lange, J. L. Boland, I. Laepple, M. Furthmeier, E. Dardanis, N. Dessmann, L. Li, E.H. Linfield, G.A. Davies, M.S. Vitiello, R. Huber, Ultrafast two-dimensional field spectroscopy of terahertz intersubband saturable absorbers, Optics Express, (2019).
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3. THz waveguide adapters for efficient radiation out-coupling from double metal THz QCLs We developed a novel approach to couple THz radiation from a double-metal QCL into an on-chip hollow rectangular waveguide feeding a triangular horn, with the specific aim of optimizing the optical beam divergence. The conceived novel extractor is composed of three parts: a series of slits patterned at the end of the laser top contact (slit coupler), a metallic waveguide section (feeder) assembled on top of the laser itself, and an adiabatic expansion of the feeder, forming a horn that radiates into an optical fiber or, alternatively, into free space.
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(a) Device schematics: yellow areas indicate metallized surfaces, gray area correspond to GaAs. (b) Scanning electron microscope (SEM) image of the cleaved chip containing two waveguide couplers; (c) SEM image of the final assembly, taken from the cleaved facet side.
References:
F. Castellano, H.L. Li, E.H. Linfield, A.G. Davies, H.E. Beere, D.A. Ritchie, M.S.Vitiello, THz waveguide adapters for efficient radiation out-coupling from double metal THz QCLs, Optics Express, 23, 5190 (2015).
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