Optical Interconnects – VCSEL’s

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VCSELS – This is one of Surface Emitting lasers where in the light is emitted in a direction perpendicular to the active region.

When we speak of optical interconnect, light source is one of the important thing to be kept in mind as they constitute the essential part in an optical Circuit. VCSEL’s pronounced as (VIXEL) is one such light source which emits light vertically and because of this fact more number of lasers can be fit in single 3″ Wafer. The best part about the VCSEL is that it can be tested at the wafer form itself thus eliminating the further manufacturing process if in case the design structure went wrong.

Structure of VCSELThe structure of a VCSEL is as follows. A pair of Bragg Mirror act as a reflectors which helps the laser in some optical cavity losses that occur as a part of laser operation. The active region is a small region consisting of few quantum wells and it is electrically pumped, the wavelength of VSCELS may be adjusted by adjusting the thickness of the reflector layers. The major advantage of VCSEL’s is that it produces an efficient monolithic light which are quite needed for the operation in optical interconnects.

Matrix arrangement of VCSELVCSELs can be implemented in a two-dimensional array, enabling a single die to comprise hundreds of individual light sources to increase maximum output power and long-term reliability.
It can also be integrated with detectors and other CMOS circuitry eliminating the needs of using only optical chip components. The wavelength of VCSEL’s are generally between 670-850nm which makes the advantage of giving bright light. Multimode VCSELs, however, can be used in applications including datacomm at data rates up to 50 Gbps as well as precision sensing applications such as encoders and 3D imaging. The optical power of VCSEL’s are also quite low, and the power required for electrical pumping is also quite around the milliwatt range. The light beam does not diverge much when compared to its competitors- LED and EED’s.

Manigandan Siva