1. MP3L David Keng, Monica Agarwal 03/17/2008
A method for constructing a compact 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 Probe 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. Flowcell – Fabrication detail
How to build this?
(a)
(b2)
(b1)
(c1)
(c2)
30 min
5 min
LIFT

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 UV glue under microscope
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