WU, Ming, MEMS Photonics, CAL, Jan 11, 2016
<p class="MsoNormal" >WU, Ming, MEMS Photonics, CAL, Jan 11, 2016</p>
<p>
he is a prof at CAL, Berkeley.</p>
<p>
This is at 4:15PM on Monday in Spilker 232 (Applied Physics) at Stfd.</p>
<p>
He jokes... everytime he is here CAL wins the Big Game (vs Stfd)</p>
<p>
he begins...</p>
<p>
consider web traffic to Facebook alone....
1.45 B monthly users growth is 13% per year;
most users are ages 18 to 25...
1.25 mobile users</p>
<p>
he shows mega data centers</p>
<p>
<b>every 60 seconds 204 M emails</b>
<b>5M google searches.</b></p>
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<b>it may take 500 machines to process a single inquiry (in Google Cloud)</b></p>
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what is a data center...?</p>
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shows a slide by Laurent Schares at IBM...</p>
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<b>largest may have 1 million sq feet and 100,000 servers....</b></p>
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servers connect to top of rack (TOR) switches...electrical...</p>
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he compares EPS = electrical packet switch vs OCS = optical circuit switch...</p>
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at 10G and 40Gbit speeds it is electrical but gets challenging when faster...</p>
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TOR = top of rack switch... to the host servers...</p>
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want to have a CORE that connects to the various TORs...</p>
<p>
HP Lab OmniSwitch... change tree structure on the fly...</p>
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available now is 3D MEMS Switch (his focus today)...</p>
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but now it is a free space switch... CALIENT is one company eg...</p>
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320 by 320 connections... only 1.5 dB loss...per connex.</p>
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but cost is abt $100 per port...</p>
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so 320 by 320 = 30 to 50 thousand dollars for a switch...</p>
<p>
<b>but we need at 10 dollar per port switch for data.</b></p>
<p>
and need thousands of ports and faster switch time
currently s at 10 to 20 ms but really want 10 to 100 microsec switch.
<b>but really want < one microsec.</b></p>
<p>
and low insertion loss ideally < 2 dB.</p>
<p>
so how abt <b>silicon photonics...</b></p>
<p>
current photonic switch is free space based...</p>
<p>
but also NTT has made 32 by 32 switch on planar lightwave circuit
but its huge abt 4 inch chip...</p>
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silicon photonics... can do billions of transistors....
commercial products available BUT <b>high optical loss and only small port counts...</b></p>
<p>
can get good switching in abt 1.3 microns to get crossover into two waveguides...</p>
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confinement of light to silicon waveguide.</p>
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shows PILOSS switch... and each node has abt 16 dB loss.</p>
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path-indep insertion loss = PILOSS.</p>
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everybody is at 0.5 dB per port...</p>
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only two ways to do switching...</p>
<p>
change refrac index by injecting holes into Si.
to modulate carrier densty
VS thermo-optic effect (eg by heating it up by hundreds of degrees.</p>
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both are very small effects...</p>
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so v inefficient...</p>
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<b>want to use MEMS instead to get 100% index modulation</b> (instead of 1% above)</p>
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no cross talk...</p>
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<b>with mems ALMOST NO OPTICAL LOSS</b>... ONLY -.01 dB at cross points...</p>
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our # of crossing is only 2N -1 .</p>
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not available as a product... <b>our students make these</b></p>
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<b>shows suspended waveguide which is 220 by 400 nm...</b></p>
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<b>uses MEMS cantilever.</b></p>
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but we have a big loss... so, what went wrong??</p>
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better to use wider waveguides...</p>
<p>
with flapping structures... (like an LA freeway on the 405...
we just mechanically lower down the entire freeway overpasses)</p>
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<b>like a flapping birds wings...</b></p>
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<b>using adiabatic couplers...</b></p>
<p>
shows a video animation... as orthogonal flaps come down the light goes thru it at right angle
instead of straight thru.</p>
<p>
uses a mechanical stopper to stop the descent of flaps...</p>
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<b>he shows 64 by 64 si photnic switch in 1 cm2.</b></p>
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unit cell size is only 110 microns sq.</p>
<p>
next he shows Gen2 switch...</p>
<p>
gap closing actuatiors...</p>
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takes abt ten volts to switch (if biased in middle of hysteresis loop)</p>
<p>
see SEOK et al in GFP in 2015 = group4 photonics conference.</p>
<p>
Seok Quack Han, et al.
reliability study...</p>
<p>
it is reliable no degrad at 10B cycles of switching</p>
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andno stiction even afger long contact...</p>
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so how to use this... (what are the apps?)</p>
<p>
multicast switch... to one to many...eg like trad. broadcast (one show eg to N users)</p>
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</p>