University of Delaware - College of Engineering
ELECTRICAL & COMPUTER ENGINEERING

Research

Photonics & Electromagnetics

High-reliability Vertical Cavity Surface Emitting Lasers (VCSEL's) and VCSEL arrays

Keith Goossen

Currently, the fastest Local Area Networks (LAN's) operate at 1 gigabit/second (Gb/s), with standards existing at 10 Gb/s. It is widely thought that within a few years, these speeds will increase first to 40 Gb/s, and that within 20 years 100 Gb/s. These networks almost universally operate with optical fiber links, lit by inexpensive Vertical Cavity Surface Emitting Lasers (VCSEL's). These semiconductor lasers are different from long-distance telecommunication lasers in that they emit light perpendicular from a semiconductor chip, rather than parallel. That is, the light comes from the top plane of the chip instead of the side or edge. This gives VCSEL's important advantages over "edge" lasers: (1) they occupy a smaller area of the chip, and so can be manufactured in larger volume; (2) the same principle allows arrays of lasers to be made; and (3) they create a circular output pattern than couples more easily into an optical fiber. While points (1) and (3) are what allow VCSEL's to be less expensive than edge lasers in current networks, point (2) is what will let them enable the 40 and 100 Gb/s networks of the future. The reason is that all lasers fundamentally degrade over time, due to the constant thermodynamic probability that when electricity is converted into light at a point in the semiconductor, that part of the crystal can suffer an atomic dislocation. This dislocation then reduces the efficiency of electricity-light conversion. Further, this probability of defect formation increases with data rate. We have projected that above a few Gb/s, degradation will occur in less than a few years; the solution is to form modules with VCSEL arrays, so that the sum of their data rates equals the required network rate. Right now 12-channel "linear" modules are under development- we are working on Nx12 2-dimensional arrays to take networks to the 100 Gb/s level.

Recent publications

K.W. Goossen, J.E. Cunningham, and A.V. Krishnamoorthy, "1x12 VCSEL Array with Optical Monitoring by Flip-Chip Bonding," IEEE Photon. Tech. Lett., vol. 18, pp. 1219-1221 (2006).

K.W. Goossen, "Optically Absorbing Metallization," Journal of Electronic Materials, vol. 34, pp. 34-36 (2005).

M. Teitelbaum and K.W. Goossen, "Reliability of Direct Mesa Flip-chip Bonded VCSEL's," Proceeding of the 2004 IEEE LEOS Annual Meeting.


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