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1 Public trial lecture: A review of the state of the art for optical computer Presented on the 6th of May 2011 Andreas Kimsås Department of Telematics 2 Agenda Introduction • Definition, Motivation, History & Classification Special purpose optical computers Linear optics, miniaturisation, application General purpose optical computer Logic classes, optical ‘’transistors’’ Quantum computer Principles, Method & Properties Summary References 3 Motivation, Evolution & Classification INTRODUCTION 4 Definition «An optical computer is a physical information processing device that uses photons to transport data from one memory location to another, and processes the data while it is in this form» – Naughton & Woods, 2009 It is not necessarily programmable It may be part of a larger (electronic) system Logic gates may be actuated using a different technology Optical transport is necessary, but not sufficient 5 Comparison optics/electronics Property Optical Electronic Information signal Photon Electromagnetic pulse Cross-talk None (free space) Yes Electromagnetic interference None Yes Parallel processing Space & frequency in the same device Space Material & information signal coupling Poor to moderate Excellent Integrated circuits Research stage Mature Gate size Limited by wavelength Quantum limit Gate speed Milli- to Picoseconds Picoseconds Fan in/out Poor to moderate Excellent Heat dissipation Debated Bottleneck 6 Optical computer research • A story of advances and setbacks Laser invented • Solid state Ruby • Pulsed operaton 1st wave 2nd wave • Quenched laser • Parallel optical logic • CW semiconductor laser at room temperature • Non-linear effects • Greater progress in other fields 1960 3rd wave • Optical fibers get commercial • Stronger nonlinearities • Weak effects • Integration • Speed 1970 4th wave 1980 5th wave • Optically switched Internet • Integrated photonic circuits • Nanotechnology • Quantum effects • Moore’s law lives on • Integration 1990 2000 7 Classification Optical Computer Signal/Image Processing Pattern recognition 3R Regenerator Numerical Processing Fourier transformation Neural Networks Analogue computing Linear algebra Digital compting Label Processing General Purpose Computer 8 Classic Linear Optics & Refinements SPECIAL PURPOSE COMPUTERS 9 Using classic linear optics • Perfect shuffle –permutes an analogue/digital address into any other adress in (logN)2 steps. • Requires additional capability of exchanging nearest neigbours • High spatial 3D paralellism • Applications • All-optical label swapping • Image analysis (rotation) Ref. & figure from Lohmann, 1985 10 Micro-lenses (lenslets) • • • Classic Lens (a) - Fresnel Zone Plate (b) – SWG (c) Subwavelength grating technical data: • Thickness 150 nm, λ=1550nm • Focal length 17.3 mm, diameter 0.3mm Applications: • Micro-scale classical optics, • Replace Bragg reflector in Vertical Cavity Surface Emitting Laser (VCSEL) Figure from Chrostowsky (2010) 11 Micro & Nano-scale devices All-optical recirculation buffer Active MZI element is a GaAs modulator Silicon waveguides on Silicon substrate MZI switches. Loop delay = 2.6m or 13 ns Ultralow threshold VCSEL laser. Threshold of 180nA @ 50K, 287nA @ 150K. GaAs active region is confined by quantum dots. Ref: Burmeister (2008), Paniccia (2010), Ellis (2011) 12 3R optical regeneration Lithographically etched, modelocked ring laser Retiming and reshaping Amplification performed by SOA Used for clock recovery in all-optical networks Ref. and figure: Koch et al. (2008) 13 Optical matrix multiplier 16 Teraflops computation capability Low power consumption (<1W) Spatial light modulator (SLM) modulated @ 125 MHz (5ns) SLM matrix is multiplied with VCSEL input vector (1x256x8bits).(256x256x8bits) Multiplication is the interaction of a vector element and a pixel Addition is the superposition of intensities Applications: Co-processor Image processing Element for: correlaton, convolution, Fourier transform, Hamiltonian path problem ++ Ref: Caulfield (2010), Tamir (2009). • 𝑎 𝑑 𝑔 𝑏 𝑒 ℎ 𝑜1 𝑐 𝑖1 𝑓 . 𝑖2 = 𝑜2 𝑜3 𝑖3 𝑘 Figure from Tamir et al. - 2009 14 Versatility of matrix multiplier General form General form (analogue or digital) Permutation, Spatial rotation & Shuffle Addition & Logical OR Multiplication & Logical AND Notes: Binary OR requires boolean interpretation of addition output. Binary AND uses the SLM matrix and input vector as inputs 15 Logic schemes & devices GENERAL PURPOSE OPTICAL COMPUTER 16 Conventional and Directed logic circuits Conventional Directed Very common in ICs of today CMOS transistor is the building block Energy is dissipated at (almost) every step Sequential stabilizaton of gates Min Clock period = longest path delay + SUM of ALL rise/fall times Inspired by Fredkin gates Cross-Bar switch is main element The same light pulse along the path, main energy cost is to set the switch All gates can be set at the same time ! Min. Clock period = longest path delay + switch reconfiguration time Refs.: Dadamundi (2005), Hardy et al. (2007) 17 Directed logic circuit examples A XOR B Initialised with True=(1,0) F(A) is cross if A=True F(A) is bar if A=False A OR B Feedback is required At most 3 levels is required to perform any logical operation Algebraic functions Not yet defined for directed logic Matrix operations ?? Refs.: Hardy et al. (2009) 18 Mechanical switch example Micro electromechanical mirror (MEMS) High spatial paralellism: 100 x100 (Fijutsu) Footprint about 8 x 6 x 3 cm3 Ref. and figures Wu & Solgaard (2006). 2x2 MEMS add-drop switch (cross-bar) 20μs switching time Collimating lenses are required for coupling Extendable to several WDM channels 19 Mechanical switch example Micro electromechanical mirror (MEMS) High spatial paralellism: 100 x100 (Fijutsu) Footprint about 8 x 6 x 3 cm3 Ref. Wu & Solgaard (2006). 2x2 MEMS add-drop switch (cross-bar) 20μs switching time Collimating lenses are required for coupling Extendable to several WDM channels 20 Guided wave switches Directed Coupler type Phased Array Switch Phase-shift e.g. via electro-optic effect. Top, three couplers, bottom Mach-Zender Interferometer Based on coupled mode theory Electronically induced phase shift Footprint 4x3 mm2 , 1x16 switch with 24 array waveguides 11 & 5 ns rise/fall time. Ref. : Caulfield (2010) & Tanamura et al. 2011 Essex M.Sc course notes 21 Other basic switching elements Description Active Passive Type Techical data On-off SOAs Couplers 2x2 GHz, noise Polarisation TFF or LCD PBS 2x2 kHz-GHz, PDL Y-junction Org. Polymer Coupler 1x2 GHz, weak nonlinearity AWJ LiNbO2 Couplers 1x2 GHz, drive voltage Thermo-electric Phase shift AWG/Couplers 1xn,2x2 kHz, slow Acousto-optic Phase shift AWG/Couplers 1xn,2x2 MHz, loss/stability Refs.: Borella (1997), Hardy (2007), Yang (2010), & Essex M.Sc. Course notes 22 All-optical SOA logic Pump, SOA and BPF is used for logic via non-linear effects (XGM,XPM & FWM) 40 GHz speed demonstrated! Cascadability demands VOA (stable output power), fast wavelength tuning, polarization control and is limited by amplifer noise. Ref. and figure: Zhang (2009) 23 Principles & Advantages QUANTUM COMPUTING 24 Basic elements Any distinguishable quantity can be used to encode the qubit value, e.g. polarisation, time bin or space State of a qubit is fully described as a sum of vector elements: a|H> + b|V>, with a2 + b2 = 1 State changed though phase shifts or by switching in space. Linear optical elements can be used without major problems (determinsitic), but loss and noise will destroy the system Non-linear effects are far too weak to be used; was the phase shift in the MZI applied or not? Refs. O’Brien (2007) & Thompson (2011). Figures from O’Brien 25 Entangled states The system should work as a CNOT gate, without using nonlinear effects. Beam splitters act on qubits inside the probabilistic gate and creates a total of 16 output combinations. The CNOT is sucessful for one combination, measured by singlephoton detection at each detector In a cascade the probability of success at all CNOTs decreases exponentially! Partily soved via quantum teleportation. If successful, the target qubit is output to the next stage. Ref and figures from O’Brien (2007) 26 Summary • Paralellism is a key property for high performance optical computing • NP to P computational complexity • Reduces footprint • Optical signal processing is useful for special purpose applications; e.g. for optical networking • The general purpose computer should not be an optical blueprint of electronic systems • Poor cascadability is currently the main impediment to general purpose optical computer • Quantum effects enables small, power-efficient and computationally efficient algorithms, but a realization is far from immediate 27 Properties of a quantum computer • • • • Power efficient Very compact (but not much smaller than other) Spatial paralellism represents a speedup Probabilistic overhead is compensated for by «quantum speedup». Ignoring overhead gives exponential speedup for some specific problems. • Identify states that correspond to a certain problem is difficult • Known applications: • Factorisation problem • Fourier transform • Probabilistic database search 28 References Naughton, T. J. and D. Woods (2009). “Optical Computing”. Encyclopedia of Complexity and Systems Science. R. A. Meyers, Springer New York 2. Lohmann, A. W. (1986). "What classical optics can do for the digital optical computer." Appl. Opt. 25(10): 1543-1549 3. Abdeldayem, H., D. Frazier, et al. (2008). «Recent Advances in Photonic Devices for Optical Super Computing». Optical SuperComputing. S. Dolev, T. Haist and M. Oltean, Springer Berlin / Heidelberg. 4. Chrostowski, L. (2010). "Optical gratings: Nano-engineered lenses." Nat Photon 4(7): 413-415. 5. Dandamudi, S. (2005). Digital Logic Circuits. Guide to Assembly Language Programming in Linux, Springer US: 11-44 6. Ellis, B., M. A. Mayer, et al. (2011). "Ultralow-threshold electrically pumped quantum-dot photonic-crystal nanocavity laser." Nat Photon 5(5): 297-300 7. Tamir, D. E., N. T. Shaked, et al. (2008). Electro-Optical DSP of Tera Operations per Second and Beyond (Extended Abstract). Proceedings of the 1st international workshop on Optical SuperComputing. Vienna, Austria, Springer-Verlag: 56-69. 8. Hardy, J. and J. Shamir (2007). "Optics inspired logic architecture." Opt. Express 15(1): 150-165 9. Wu, M. C., O. Solgaard, et al. (2006). "Optical MEMS for Lightwave Communication." J. Lightwave Technol. 24(12): 4433-4454. 10. Caulfield, H. J. and S. Dolev (2010). "Why future supercomputing requires optics." Nat Photon 4(5): 261263. 11. Borella, M. S., J. P. Jue, et al. (1997). "Optical components for WDM lightwave networks." Proceedings of the IEEE 85(8): 1274-1307. 12. Yang, W., Y. Liu, et al. (2010). "Wavelength-Tunable Erbium-Doped Fiber Ring Laser Employing an Acousto-Optic Filter." J. Lightwave Technol. 28(1): 118-122. 1. 29 References II 13. Koch, B. R., A. W. Fang, et al. (2008). All-Optical Clock Recovery with Retiming and Reshaping Using a Silicon Evanescent Mode Locked Ring Laser. Optical Fiber communication/National Fiber Optic Engineers Conference 14. Paniccia, M., (2010), Integrating silicon photonics, Nature Photonics, Interview | Focus, Vol. 4. 15. Burmeister, E. F., J. Mack, et al. (2008). SOA Gate Array Recirculating Buffer for Optical Packet Switching, Optical Society of America 16. Zhang, X., J. Xu, et al. (2009). All-Optical Logic Gates Based on Semiconductor Optical Amplifiers and Tunable Filters. Optical SuperComputing. S. Dolev and M. Oltean, Springer Berlin / Heidelberg. 5882: 1929. 17. Tucker, R. S. (2006). "The Role of Optics and Electronics in High-Capacity Routers." Lightwave Technology, Journal of 24(12): 4655-4673 18. Thompson, M. G., A. Politi, et al. (2011). "Integrated waveguide circuits for optical quantum computing." Circuits, Devices & Systems, IET 5(2): 94-102 19. O'Brien, J. L. (2007). "Optical Quantum Computing." Science 318(5856): 1567-1570 30 Optical label processing • • Klonidis et al. Muligens 1 slide av Leuthold