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A method for constructing a compact flowcell – using short taper coupling

A method for constructing a compact flowcell – using short taper coupling. MP3L David Keng, Monica Agarwal 03/17/2008. Overview. Flowcell requirements Previous What to change? How to change? New design Fabrication Result Conclusion. Flowcell Requirements. Contains Microsphere

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A method for constructing a compact flowcell – using short taper coupling

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  1. A method for constructing acompact flowcell – using short taper coupling MP3L David Keng, Monica Agarwal 03/17/2008

  2. Overview • Flowcell requirements • Previous • What to change? • How to change? • New design • Fabrication • Result • Conclusion

  3. Flowcell Requirements • Contains • Microsphere • Coupling Fiber • Inlet / Outlet • Dimension • Small size overall • Small overall dimension tolerance • Previous flowcell design

  4. Flowcell – previous • To contain the coupling fiber • Flowcell has to cover the effective length of the fiber • This length is usually > 10 mm • Overall volume ~ 20 mm3 minimum • Contains only one microsphere • Difficult to contain more • Dips only and high Q not easy to track • Require exact phase matching to couple • Difficult to couple high index microspheres • What to change?

  5. What to change? Design Goal • Smaller size • Multiple microsphere • An easy way to locate high Q WGM • Possible solution for high refractive index microsphere coupling (why?) • How?

  6. How to change? • Use a fiber taper instead • Short effective length ~ 300 micron • Phase matching not as crucial • Another pick up fiber to detect peaks • Use an array of these fiber tapers • Multiple microsphere coupling • Should have at least one reference sphere

  7. Reference microsphere • Common noise rejection • Thermal drift of cell • Difficult to compensate • Thermal drift of laser • Require a high Q wavelength reference • TTL triggering delay • Can be compensated, but cannot be eliminated • Non-specific binding • Can only be detected by another microsphere • Reference microsphere • Should solve the problems above • New design

  8. Fiber taper coupling • Pump – probe configuration • Pump fiber • Excite WGM • Probe fiber • Sample WGM

  9. Flowcell – new design • Multiple pump-probe pairs • In this case, 2 • Allows two microspheres to be coupled • Within 800 microns of each other • Why this configuration?

  10. Flowcell – Planar configuration • Planar design • Low profile = small flowcell volume • Semi-automatic alignment • Microsphere coupling relatively easy

  11. Flowcell - Fabrication • Meniscus • Forms between 2 liquids • Height = Radius-1 • Creates a taper • This technique • Well established • Near field probe Silicone oil (PDMS) 48% HF acid

  12. (a) (b1) (b2) (c1) (c2) 5 min 30 min LIFT Flowcell – Fabrication detail • How to build this?

  13. Fabrication result • Smooth linear taper • Only the cladding is etched! • Propagation unchanged • Low loss <50% • Possibly due to the meniscus profile 8 micron /div 4 micron

  14. Assembling • Check fiber diameter • Fine etch to adjust diameter • UV glue under microscope • Allows time to align • Apprx. 50 micron gap between the two pairs

  15. Result • Q ~ 106 with zero background in water • Peaks can be easily tracked • Detector gain offset

  16. Conclusion • Low loss taper fabrication SOP established (15 days) • Multiple fiber SOP established (10 days, with Monica) • Assembling SOP established (3 days) • Fabrication and assembling takes ~1hr • <20 micron tolerance un-jacketed region • <1 micron tolerance on effective region diameter • Same coupling apparatus as before • Original concept 02/8/2008 (40 days) • To do: • Testing flow noise • Attempting higher refractive index microsphere coupling

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