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Overview of new ultrafast research initiative within ODM Research Group University of Surrey Jeremy Allam School of Physics and Chemistry Optoelectronic Devices and Materials Research Group Guildford, Surrey GU2 7XH, UK Tel +44 (0)1483 876799 Fax +44 (0)1483 876781 ODM ultrafast optical communications Terabit/second optical networks are here! • • SOA-based optical switches for all-optical network limited above ~100Gbit/s by intraband carrier dynamics ODM ultrafast ultrafast revolution ultrafast opto-electronics microwave photonics electrooptic sampling THz device physics NL pulse propagation nonlinear optics highharmonic ultrashort (<10fs) generation biological / solid-state intense (UV, X-ray) tunable femtosecond environ(>1TW) (UV-MIR) mental lasers relativistic sensing optical electron coherent spectromotion scopy non-stochastic coherent breakdown control controllable material ablation photoprocessing chemistry medical applications free-space THz highenergy physics ODM ultrafast aspects of research at Surrey (1) bandstructure engineering of material / device dynamics • theory (beyond effective mass) • design (optimise device dynamics) • diagnostics (high-pressure experiments) (2) advanced experimental and theoretical methods • femtosecond lasers, OPOs, OPA; FELIX • broadly-tunable, ultrashort, high-intensity light pulses • comprehensive, first-principles theoretical models (3) femtosecond physics in advanced real-world devices (4) convergence of optics and electronics • interband • optical transitions • high-speed photonics • ultrafast optics AND AND AND AND intraband dynamics electron transport microwave electronics mid/far-infrared spectroscopy (5) time + frequency domain characterisation • (ω,τ) optical methods (e.g. FROG) for amplitude, phase dynamics • electro-optic sampling for THz device / circuit characterisation • optical pulse shaping for all-optical bit-error-rate measurement? ODM ultrafast research activities (1) Mid-infrared time-resolved experiments - FELIX Dr. Ben Murdin (2) Theory of ultrafast interactions in semiconductors Dr. Steve Hughes (3) Ultrafast optical / electronic devices Prof. Jeremy Allam 1996 1997 1998 1999 2000 2001 2002 1 4 7 10 1 4 7 10 1 4 7 10 1 4 7 10 1 4 7 10 1 4 7 10 1 4 7 10 BNM SH JA fs experiments ATI start occupation ODM ultrafast research activities 1 (1) Experimental studies of intersub-band transitions and mid-infrared devices - Dr. Ben Murdin (i) Mid-infrared lasers (ii) Time Resolved spectroscopy with FELIX (iii) New infrared materials: InSbN ODM ultrafast Electrically pumped semiconductor laser Conventional interband device Small, low cost, rugged Pollution monitoring, process control etc applications Mechanisms preventing room temperature operation Mid-infrared lasers Elastic collisions between charges (Auger effect) valence band absorption phonon emission (=heat!) Quantum Cascade device C O Solution = band-structure engineering quantisation strain ODM ultrafast Spectroscopy with FELIX Free Electron Laser for Infrared eXperiments, Utrecht, NL Tuneable from 4 -250mm!! 1MW peak power!! Pulses only 6 optical cycles!!! Example experiments: Pure and applied physics scattering/recombination times between charges on femtosecond scale searching for excited states in new materials like quantum dots, polymers, buckyballs new fundamental regimes of ultra-short times and ultrahigh a.c. electric fields ODM ultrafast New infrared materials: InSbN Adding dilute N to III-V semiconductors gives strong bandgap bowing (energy decreases) long l emission from wide-gap constituent materials electron effective mass increases, suppressing Auger pump-probe using FELIX shows lifetime in an InSbN sample with 11mm gap () is much longer than for HgCdTe of same gap and same excitation (—) [only slightly faster than InSb (···) and HgCdTe with 7mm gap (- -)] Normally Auger increases exponentially with reducing gap 1.00 D T/T (arb. units) 0.37 290K 0 200 400 probe delay (ps) 600 ODM ultrafast research activities 2 (2) Fundamental theory of ultrafast electron-photon interactions in semiconductors - Dr. Steve Hughes • many-body quantum theory of semiconductor optics: • Rabi flopping, excitonic trapping • inverted semiconductors • pulse reshaping in SOAs • modulation of lasers and SOAs through THz field • Few-cycle optical pulse propagation • beyond slowly-varying envelope approximation • Extremely-excited states • fs optical pulse, THz field, magnetic field • dynamic Franz-Keldysh effect • magneto-excitons - dancing with wavepackets ODM ultrafast theory of inverted semiconductors previous: • Rate Equation Model (REM) • phenomenological NL gain and saturation* • adiabatic light-matter interaction *via: two-photon absorption (TPA), free-carrer absorption (FCA), spectral hole burning (SHB), carrier heating (CH) but experiments on SOAs show: • coherent effects (phase storage) • non-transferable NL parameters so use a first-principles, microscopic approach: • semiconductor Maxwell-Bloch equations • diagonal and non-diagonal dephasing • many-body carrier-carrier interactions state-of-the-art description of semiconductor gain future improvements: • band-structure effects • non-Markovian dynamics ODM Extremely excited ultrafast wavepackets • newly available sources (Terawatt lasers, ultrashort pulse lasers, free-electron lasers...) allow extreme excitations • theoretical treatment requires non-perturbative, many-body quantum approach...... and reveals new phenomena optical excitation + THz field + magnetic field dancing wavepackets ODM ultrafast research activities 3 (3) Ultrafast measurements of optical and electronic devices - Prof. Jeremy Allam • optoelectronic devices: lasers and SOAs • fs pulse propagation in semiconductor LD - ‘solitonic dark pulses’ • key questions: • How to modulate lasers faster? • How to increase bandwidth of all-optical switch? • ultrafast photodetectors: • ultrafast photoconductors • TW-WG PD/PT (with Prof.’s Robertson and Weiss) • dynamics of impact ionisation (with Sheffield) • mid-infrared dynamics • dynamics dominate CW performance... • compare interband, type II and intraband (QC) devices • ultrafast electronics • THz electro-optic measurements of devices and circuits • new concepts for THz electronics ODM ultrafast current modulation of lasers electro-absorption mid-infrared (Gorfinkel ‘92) optical pulse (Elsaesser ‘97) THz pulse (Hughes ‘98) intraband processes ODM ultrafast optical switch dynamics desired response Modulator Df MZ p t SMZ actual response bandstructure engineering of dynamics? ODM Ultrafast laser experiments mid-IR near-IR visible ODM