InP-based VCSELs in the 1.4 to 2 μm wavelength range for optical communication and absorption spectroscopy

Abstract

Phone: +49 (0)89 28912780, Fax: +49 (0)89 3206620, Email: mcamann@wsi.hrm.de, VRL: www.wsi.tum.de M. Lackner and F. Winter ProcessEng Engineering GmbH Pos fach 30, A-2500 Baden, Austria Phone:+43 (0)2252254466, Fax:+43 (0)2252254440. Email:lackner@processeng.at, URL:www.processeng.at Abstract: With the blaied hrnnel junctions technology a breoldhmugh in the dynamic and stationay lasing performance has been achievedfir long-wavelength In!-based VCSELr making these lasers iakally suiledfor broadband communications andgas sensing applications.lntrodueiion Long-wavelength VCSELs are of very high interest for future short and mid range optical interconnects as well as for gas sensing applications. However, the commercialition of long-.wavelength VCSELs has been seriously delayed by several technological challenges, particularly the lack of suitable InP-based mirrors. While the proven GaAs-VCSEL technology extends to 1.3 pm exploiting GaInNAs active regions [l], this concept seems unlikely to cover wavelengths beyond 1.3 pm with reasonable performance. For this range, numerous approaches have been reported in the past few years [2,3]. TechnologyThe best results to date particularly regarding output power, operating temperature and dynamic behavior have been achieved with monolithically grown InGaAlAs/InP buried tunnel junction (BTJ) VCSELs [4] as shown in Figure 1.The BTJ enables both current and index confinement and leads to significantly lower series resistances. In addition, optimized heatsinking capabilities are accomplished by an InF' heat spreading layers, a short period dielectric bottom Figure 1: (a) Cross-section of BTJ-VCSEL. (b) Fully processed 2-inch wafer with M)M) laser units.mirror stack as well as an integrated Au heatsink. It should be noted that all processing steps are fully compatible with full wafer manufacturability. By adjusting mirror layers and active regions, the InPbased lasers allow for versatile applications at different wavelengths. Besides the typical telecommunication wavelengths at 1.31 and 1.55 pm, BTJ-VCSELs could even demonstrate reasonable room-temperature cw performance beyond 2 pm wavelength [6]. ApplicationsIn the high volume access market, VCSELs may play an important role in optical links. However, fulfilling all of the performance requirements is an ongoing challenge. To date, BTJ-VCSELs have demonstrated up to 110°C cw operating temperature, 1 mW single mode and 7 mW multimode output power @ 20°C and high modulation capability as shown in Figure 2(a). Even better performance is expected with furtber improvements of heat sinking, reduction of parasitic capacities and modified waveguiding to enable single mode emission at larger aperhlres. Besides optical interconnects, significant market potentials for long-wavelength VCSELs also arise from applications in the field of tunable diode laser absorption spectroscopy (TDLAS). The increasing need for environmental surveillance, process control or trace gas detection requires suitable detection 0-7003-7000-1/03/$17.00@2003 IEEE 505