Background on Gigabit Ethernet ECE 4006 C G3: Karen Cano, Scott Henderson, Di Qian Dec,

Ethernet History (Timeline) 1973 – (2.94Mbps) First developed at Xerox’s Palo Alto Lab (Robert Metcalfe and David Boggs) (10Mbps) Improvement by DEC, Intel and Xerox. The DIX standard. Thick Ethernet System Formally standardized as IEEE 802.3

Timeline (con’t) 1983–1989 – Improvements on bus topology and transmission distance – version IEEE 802.3i, 10Base-T technology (100Mbps) version IEEE 802.3u, also call “Fast Ethernet”.

Timeline (con’t) 1998 – (1 Gbps) version IEEE 802.3z, fiber optics; and IEEE 802.3ab, twisted pair. Also know as “Gigabit Ethernet”. Present – (10 Gbps) standard completed in 2002.

Project Tasks 1. Research on the transmitting and receiving modules. 2. Examine the testing board 3. Search for the components 4. Testing the evaluation board with purchased components 5. Connecting the purchased components with parts from other groups.

Project Goal Duplicate the data transmitting and receiving module functionality of the Gigabit Ethernet technology with purchased components that provide optimum performance at a minimum price.

Possible Solutions Transmitting module (laser source) –VCSEL Receiving module (Photo-detector) –PIN photodiode Other Specs: - SC connectorized (optical) - SMA connectorized (electrical) - 850nm - Multimode (fiber) - relatively low cost

Laser Basics What is a Laser? –Light Amplification by Stimulated Emission of Radiation How? 1) Electrons in low-energy levels bumped into high levels by injection of energy 2) When an electron drops to a lower energy level, excess energy is given off as light.

VCSELs Vertical Cavity Surface Emitting Lasers Physical makeup –Bragg mirrors –Active region Fabrication techniques –Molecular beam epitaxy –Vapor phase epitaxy

VCSELs In EELs no pre-cleaving tests can be performed, testing VCSELs is much cheaper Less current required for VCSELs Output beam easier couple into fiber and much less divergent than EELs Smaller and faster than EELs

VCSELs vs. EELs Edge Emitting Lasers - give out their light from the sides or edges, therefore no pre- cleaving tests can be performed Since VCSELs emit light from the top and bottom, they do not have this problem. Testing them is much cheaper

Interesting Facts In a typical VCSEL, as many as 60 individual semiconductor layers are stacked within a structure 10 microns thick. 20,000 individual laser die can be fabricated on a single 3 inch wafer.

Multimode Multimode- light is injected into the core and can travel many paths through the cable (i.e. rattling in a tube). Each path is slightly different in length, so the time variance this causes, spreads pulses of data out and limits the bandwidth.

Singlemode Fiber has such a narrow core that light takes one path only through the glass. Not limited to modal-bandwidth. Very small amount of pulse-spreading is consequential only in Gigabit speed applications.

Photodetectors Necessary for light pulse detection Wide variety of of types –Photoconductors –Avalanche photodiodes –PIN photodiodes –MSM photodiodes

Photoconductors Operation based on varying conduction Many important factors affecting bandwidth –Transit time –Surface area of photon acceptor region –Noise ratio (Johnson noise) –Quantum efficiency

Avalanche Photodiodes Exemplify the “gain-bandwidth” tradeoff Use the p-n junction model to operate Take advantage of the avalanche effect –Carrier multiplication –Associated gain –Time constant associated with avalanche –Bandwidth penalty

PIN Photodiode PIN –Reason for name –Doped region, undoped region, doped region –Unity gain –Functions under reverse bias Most important parameter for operation –Transit time

Bandwidth vs. Depletion Width Transit time –Time for subatomic particle to get from one electrode to the other Based on quickest, typically electron –e - mobility > h + mobility Capacitance limited

Transit Time (continued) Dependence on intrinsic region length Minimizing this region High bandwidth applications

MSM Photodiode Metal-Semiconductor-Metal –Associated work functions –Atomic level metal-semiconductor marriage High speed (up to 100GHz) Majority carrier devices Not developed for Gigabit Ethernet on scale as large as PIN

Concluding, thus far….. Obvious choices for devices: –PIN photodiode w/ acceptable bandwidth –Multimode fiber –SC optical connectors –SMA electrical connectors Gigabit Ethernet is a popular application If you are buying less than five-million devices then be prepared to stand at the end of the line.