ODMODM Overview of new ultrafast research initiative within ODM Research Group Jeremy Allam Optoelectronic Devices and Materials Research Group Tel +44 (0) Fax +44 (0) University of Surrey School of Physics and Chemistry Guildford, Surrey GU2 7XH, UK

ODMODM optical communications Terabit/second optical networks are here! SOA-based optical switches for all-optical network limited above ~100Gbit/s by intraband carrier dynamics ultrafast

ODMODM ultrafast revolutionultrafast

ODMODM 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 AND intraband dynamics optical transitions ANDelectron transport high-speed photonics AND microwave electronics ultrafast optics AND 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? ultrafast

ODMODM 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 JA ATI occupation fs experiments start SH BNM ultrafast

ODMODM research activities 1 (i) Mid-infrared lasers (ii) Time Resolved spectroscopy with FELIX (iii) New infrared materials: InSbN (1) Experimental studies of intersub-band transitions and mid-infrared devices - Dr. Ben Murdin ultrafast

ODMODM Mid-infrared lasers Electrically pumped semiconductor laser Small, low cost, rugged Pollution monitoring, process control etc applications Mechanisms preventing room temperature operation Elastic collisions between charges (Auger effect) valence band absorption phonon emission (=heat!) Solution = band-structure engineering quantisation strain Conventional interband device Quantum Cascade device C O ultrafast

ODMODM Spectroscopy with FELIX Free Electron Laser for Infrared eXperiments, Utrecht, NL Tuneable from mm!! 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 ultra- high a.c. electric fields ultrafast

ODMODM New infrared materials: InSbN Adding dilute N to III-V semiconductors gives strong bandgap bowing (energy decreases) long emission from wide-gap constituent materials l electron effective mass increases, suppressing Auger ultrafast pump-probe using FELIX shows lifetime in an InSbN sample with 11  m gap ( ) is much longer than for HgCdTe of same gap and same excitation (—) [only slightly faster than InSb (···) and HgCdTe with 7  m gap (- -)] l Normally Auger increases exponentially with reducing gap

ODMODM 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 ultrafast

ODMODM theory of inverted semiconductors ultrafast previous: Rate Equation Model (REM) phenomenological NL gain and saturation* adiabatic light-matter interaction coherent effects (phase storage) non-transferable NL parameters so use a first-principles, microscopic approach: *via: two-photon absorption (TPA), free-carrer absorption (FCA), spectral hole burning (SHB), carrier heating (CH) but experiments on SOAs show: semiconductor Maxwell-Bloch equations diagonal and non-diagonal dephasing many-body carrier-carrier interactions future improvements: band-structure effects non-Markovian dynamics state-of-the-art description of semiconductor gain

ODMODM 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

ODMODM 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 ultrafast

ODMODM modulation of lasers ultrafast current electro-absorption optical pulse ( Elsaesser ‘97) mid-infrared (Gorfinkel ‘92) THz pulse (Hughes ‘98) intraband processes

ODMODM optical switch dynamics ultrafast Modulator MZ actual response desired response SMZ bandstructure engineering of dynamics?

ODMODM Ultrafast laser experiments mid-IR visible near-IR