BTG seeks VCSEL strain compensation
The Strain-Compensated Multiple Quantum Well technology overcomes the critical thickness constraint that restricts the wavelength range of VCSELs. The strain compensation allows many quantum wells to be stacked to form the gain medium without undue strain buildup. This dramatically improves the performance of the VCSEL.
VCSELs are constructed by sandwiching the laser gain medium, or active layer, between two stacks of alternating high and low refractive index mirrors – creating a distributed Bragg reflector (DBR).
The multiple quantum wells (MQWs) are extremely thin layers of Group III-V compound semiconductor material used as the gain medium. Straining the MQW layers improves the VCSEL performance. However, it has been difficult to stack a sufficient number of strained quantum wells to achieve the gain needed for long wavelength VCSELs due to the critical thickness constraint. When the thickness of the strained quantum wells exceeds this thickness, dislocations and other defects are formed between the quantum well layers. The result is significant compromise in the performance of the device.
VCSELs are seen as extremely attractive for telecom and datacom applications due to the lower power consumption of the technology, compared with edge-emitting lasers. VCSELs also have potential for high-volume manufacturability, simple two-dimensional array fabrication, superior beam quality and less complex test.
At the 850nm wavelength, VCSEL-based transceivers have become the dominant laser communications solution for high-speed, very short-reach (VSR) optical interconnects, such as Gigabit Ethernet and Fibre Channel. Longer wavelength VCSELs operating at 1300nm and 1550nm increasingly appeal to transceiver producers of short and intermediate reach SONET/SDH and Fibre to the Home (FTTH) applications. Parallel VCSEL transceivers could attract back-plane interconnect applications.
"The telecom market is looking for a next generation technology that will replace costly, low yield devices, such as distributed feedback (DFB) lasers at 1300nm and 1550nm wavelengths," says Jay Kshatri, vice-president of BTG's Semiconductors & Optoelectronics business unit. "We believe that the strain-compensated VCSEL is that technology and we are actively seeking licensees who are interested in integrating this technology into their commercial products."
BTG finds, develops and commercialises emerging technologies in the life and physical sciences. The company traces its origins to 1949. BTG has commercialised technologies such as magnetic resonance imaging (MRI), recombinant factor IX blood-clotting protein, Campath (alemtuzumab) and multilevel cell (MLC) memory.
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