Real-time active alignment using mechanical dynamics of optical interconnection systems Makoto Naruse (1)(2), Alvaro Cassinelli(3), Masatoshi Ishikawa(3) 1: Communications Research Laboratory, 4-2-1 Nukui-Kita, Koganei, Tokyo 184-8795, Japan Phone: +81-42-327-6209 Fax: +81-42-327-7035 Email: [email protected] 2: Japan Science and Technology Cooperation, PRESTO 3: University of Tokyo Dept. Information Physics and Computing 7-3-1 Hogo, Bunkyo, Tokyo 113-8656, Japan Abstract Real-time active alignment for short-distance optical interconnections is demonstrated by taking into account most mechanical properties of the optical hardware. Alignment performances has been successfully controlled by considering internal and external mechanical properties of the interconnection system (such as micro-actuator dynamics or disturbance), with the aid of H-infinity control theory. Contents •High density parallel optical interconnection fabric •Dynamic alignment / switching technology Control Theory for optical interconnection systems (H-infinity theory) Simulation ／ Experimental system／Experimental results Parallel high-density interconnection • High-bandwidth, low-latency optical interconnections inter-computers, boards, or VLSI chips • Interconnection fabric, switching fabric High-parallelism demanded by two-dimensional (2D) parallelism Alignment issues High-density parallel interconnect fabric / switching fabric Alignment is one of the critically important issues Methods Passive alignment Redundant alignment Real-time Active alignment Mechanical dynamics and Optical interconnects Active alignment or optical switching: Using mechanical dynamics Real-time control HISTORY Static：Alignment tolerance analysis Dynamic： •Insertion control (NTT) (JLT, Vol. 15, pp. 874–882, 1997) •MEMS optical switch •Active alignment using PID control methods (University of Tokyo) (PTL Vol. 13, pp. 1257-1259, 2001) Dynamics in optical interconnection systems Parallel optical channels (input) = VCSELs, Fibers, Free-space, etc Disturbance（s） Parallel interconnection / Switching block (Free-space / 2D Guided wave) Actuator（s） Sensor（s） Parallel optical channels (output) Desired specification Dynamic properties Two-dimensional High-density Channels Performance we want for active systems Disturbance compensation Mechanical-based Optical switching Active alignment Fast transition between status Modeling of the system GOAL Design the controller that doesn’t transfer disturbance w to the misalignment y Disturbance Control input u w Active alignment actuator Controller ＋ ＋ Misalignment y Using H-infinity control theory Disturbance w(s) Generalized Plant Control variable z (s) G (s) Control input u (s) Output variable y (s) Controller K (s) GOAL z ( s) ( s) w( s) Influence from Disturbance to Control variable Make this as small as possible Using H-infinity control theory (cont.) F F sup H infinity control theory derives a controller K(s) so that is small. Fu u L2 L2 A framework of active alignment system (Virtual) Disturbance dynamics Disturbance w W Control variable z Actuator Control input u ＋ P － z( s) w( s) y ( s) G( s) u( s) Output variable W G 1 y WP G Experimental system Vibration generator Disturbance Dynamics W (s ) ～ VCSEL VCSEL Vibration generator Interconnection optics Interconnection optics Quadrant photodetector Misalignment error Piezo actuator H∞ controller K (s) Quadrant detector Controller (PC) Piezo microstage Control signal Active alignment actuator dynamics P(s ) Specifications VCSEL : Roithner TMC-4A (Wavelength: 850nm) Quadrant Detector : Hamamatsu S2544 (1mmφ, 20mm gap) AD/DA Converter : National Instrument PCI-MIO-16E-4 Personal Computer : DELL OptiPlex GX200 Sampling Rate : 200ms Vibration Generator : Wilcoxon Research F5B/Z11 Interconnection Optics: 4f lens system (Spindler&Hoyer f 100 plano-convex) Disturbance dynamics 1.2 4.532 e4 W ( s) 2 s 95.2 s 2.266 e5 1 Gain[a.u.] 0.8 0.6 0.4 Experimental 0.2 0 30 40 50 60 70 Frequency[Hz] 80 90 100 110 Actuator dynamics P ( s) 4.532 e4 s 2 95 .2 s 2.266 e5 Performance evaluations（simulation） Compensate the disturbance with respect to its dynamical property. Gain from disturbance d to misalignment y Bode Diagram Magnitude (dB) -80 -85 -90 -95 180 Phase (deg) Disturbance concerned Cf Disturbance dynamics not concerned 135 90 45 0 20 30 40 50 60 Frequency (Hz) 70 80 90 100 Experiment Virtually giving several sets of disturbance dynamics Observe corresponding active alignment performance disturbance dynamics W1 ( s) 0 Magnitude (dB) Low frequency enhanced W2 ( s) W1 ( s) -1 -2 s 1 2 100 -3 -4 High frequency enhanced -5 30 Phase (deg) 1 s 1 2 50 W2 ( s ) s 1 2 100 0 -30 -60 10 20 30 40 50 60 Frequency (Hz) 70 80 90 100 Experimental Results Reduction ratio = Amplitude of the misalignment: Active alignment operated Amplitude of the misalignment: Active alignment not operated 1.4 Reduction ratio 1.2 1 W2 ( s) 0.8 W1 ( s) 0.6 0.4 0.2 0 0 20 40 60 80 100 Frequency [Hz] 120 Dynamical property appeared in the active alignment performance 140 160 Summary • Theory for dynamic optical interconnection system shown. • It concerns most of mechanical dynamics such as disturbance or actuator dynamics with the aid of Hinfinity control theory. • Experimental results shown Future prospect Adapt to real application systems such as interconnection fabric, optical crossconnect (OXC) among others
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