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Optical Channel Monitor

Optical Channel Monitor. Liang-yu Chen Jian Li Arvind Narayanaswamy Dilan Seneviratne Zhenhai Zhu Mentored by Prof. George Barbastathis. Outline. Introduction Grating Design Actuator Fabrication Sub-components Drive signal Assembly and alignment Summary. Goals. Device

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Optical Channel Monitor

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  1. Optical Channel Monitor Liang-yu Chen Jian Li Arvind Narayanaswamy Dilan Seneviratne Zhenhai Zhu Mentored by Prof. George Barbastathis

  2. Outline • Introduction • Grating Design • Actuator • Fabrication • Sub-components • Drive signal • Assembly and alignment • Summary

  3. Goals Device • Monitor optical power in fiber carrying WDM signals Applications • Real-time optical performance monitoring of DWDM networks • Optical add/drop monitoring and diagnostics • EDFA gain balancing

  4. Design Requirements • Scan 10 wavelengths (l1 … l10) in 10ms • 5% diffraction efficiency • Central wavelength: 1.5mm • Operate under 50V • +/- 10% variation between l1 and l10

  5. Device concept

  6. Grating operation actuator grating

  7. Outline • Introduction • Grating Design • Actuator • Fabrication • Sub-components • Drive signal • Assembly and alignment • Summary

  8. t 1 x 0 s p f fo x 0 s p Grating design • Type of grating - amplitude or phase • Pitch and spacing between beams (nominal duty cycle) Amplitude grating Phase grating

  9. -1 -2 0 -1 0 +1 +1 Grating Design • Angle of incidence • Thickness of beams Normal incidence Incidence at an angle

  10. l3 l4 l5 l6 l7 l4 l5 l6 Design challenges • Focusing on the detector • spot size • spot overlap detector

  11. ln-1 ln ln+1 Design challenges • Focusing on the detector • spot overlap

  12. Overview of the Whole Device • Large number of grating beams needed • Natural Frequency is too low • Split into pieces • Efficiency reduction caused by comb drive and space between two pieces

  13. Outline • Introduction • Grating Design • Actuator • Fabrication • Sub-components • Drive signal • Assembly and alignment • Summary

  14. Lumped model • Resonant frequency >1khZ, for fabrication limitation and operation limitation Grating Design

  15. Grating Design (2) • Resonant frequency • Grating beam: 4khZ • Whole system: 1.5khZ • Number of gratings for each piece: N=500 • Displacement of the gratings: N*22.5nm=11.3um • Actuation force Needed: k*22.5nm=53uN

  16. Actuator • Requirements: • Displacement: 11.3um • Force 53mN • Voltage 0-50V • Options: • Electrostatic: Ease of fabrication, Low power, high stroke • Piezoelectric: Low strain • Thermal: High power, long response time

  17. Electrostatic Actuators • Electrostatic actuators - ease of fabrication • Different electrostatic actuators • Comb Drive • Capacitor Plate • Zipping Actuator

  18. Electrostatic Actuators (2) • Force Displacement curve

  19. Results • Displacement 20um • Force 255uN @ 50V • 4 times larger than needed • Can be used to calibrate the device • Air damping: quality factor Q ~ 30

  20. Outline • Introduction • Grating Design • Actuator • Fabrication • Sub-components • Drive signal • Assembly and alignment • Summary

  21. Fabrication: overview Two masks, SOI wafer, KOH back etch

  22. SOI HF wet etch strip PR DRIE KOH etch Silicon Oxide Silicon Photo Resist Fabrication

  23. Outline • Introduction • Grating Design • Actuator • Fabrication • Sub-components • Drive signal • Assembly and alignment • Summary

  24. Detector • Sensitivity – flat response at 1.5mm 1.49625 m to 1.50375 m 1.5m

  25. Lenses • Collimating system • Lenses • Transmission - > 99.5%

  26. f2 f1 Lenses (2) • Magnification system • M = 22 = f1/f2 = 44mm / 2mm • Bi-convex • EFL - 44 mm • Bi-concave • EFL - 2 mm

  27. Outline • Introduction • Grating Design • Actuator • Fabrication • Sub-components • Drive signal • Assembly and alignment • Summary

  28. From Axsys Technologies Assembly and Alignment • Requirements: • Tolerances permissible by design • Perpendicular to optical axis – 0.2 – 0.4 mm • Along optical axis - 0.8mm • Precision achievable by assembly – +/- 10nm • Assembly outsourcing • Axsys Technologies • Zygo -

  29. Calibration l1 Detector ql l10 qS Detector plane qS Total swing possible ql Total swing required Total permissible error = (qS - ql)/2

  30. Calibration (cont.)

  31. Outline • Introduction • Grating Design • Actuator • Fabrication • Sub-components • Assembly and alignment • Drive signal • Summary

  32. Drive Signal

  33. 110/ 60 AC/ DC Drive Signal (Cont.) 50V 3.3V AC/ DC Oscillator + + 110/ 60 - -

  34. 110/ 60 AC/ DC Drive Signal (Cont.) 50V + -

  35. Conclusion(s) Central wavelength: 1.5mm Scan 10 wavelengths in 10ms 5% diffraction efficiency (+/- 10%) Operate under 50V Device size - ~ 10cm X 10cm Easily calibrated Minimum alignment In-expensive fabrication

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