Abstract ― Vertical cavity surface-emitting lasers (VCSEL) with etched holes surrounding a central lasing region are shown to exhibit improved single mode output power than previous photonic crystal VCSELs that lacked an optimization of the oxide aperture placement. Over 3.1 mW is obtained in this study.
High power output in a single mode laser is important for optical communications systems, sensing applications, and free space optical interconnects. Holes etched into the top distributed Bragg reflector of a vertical cavity surface-emitting lasers in a triangular pattern surrounding a central lasing area have been shown in the past to enable reproducible and predictable operation in the fundamental lateral mode. 1) Here, the placement of the oxide aperture is optimized to increase the amount of power available from the devices. By allowing the oxide aperture to encroach upon the central lasing region, the threshold current and maximum output power improve. 3.1 mW of output power in the fundamental mode was obtained through the optimization.
Fig. 1 illustrates the basic design of the device, which was fabricated here with two different central lasing aperture sizes, based on their single mode properties predicted by a photonic crystal model treating the holes as index steps and accounting for the finite etch depth. 2) The oxide aperture placement is varied to maximize the single mode power, defined as having at least 30 dB side mode suppression. 3) The results of the study are shown in Fig. 2. As the oxide aperture width approaches the central lasing aperture size in each case, the index step is perturbed and the holes no longer present sufficient loss to prevent oxide confined modes from lasing. In spite of this limitation on smaller oxide aperture sizes, over 2 mW single mode output power was obtained. When a design of 10 µm oxide aperture and 6.7 µm central lasing aperture was transferred to a wafer designed for higher power conversion efficiency, 3.1 mW of output power in the fundamental mode was obtained as shown in Fig. 3. In addition, devices tested on this material showed 9 GHz small signal modulation 3 dB bandwidths.
The dependence of the etching depth on the single mode property of the device is not great, thus this method of producing single mode devices is straightforward and can be applied to virtually any material system to reproducibly yield single mode devices with high powers and reasonable bandwidths.
References
D. S. Song, S. H. Kim, H. G. Park, C. K. Kim, and Y.H. Lee, Appl. Phys. Lett., 80, 3901-3903 (2002).
N. Yokouchi, A.J. Danner, and K.D. Choquette, J. of Sel. Topics in Quant. Elect., 9, 1439 (2003).
A.J. Danner, J.J. Raftery, Jr., and K.D. Choquette, CLEO 2004, Paper CTuP13, San Francisco, CA.