Heterogeneously integrated long wavelength VCSEL based transceivers for data center networks

Semiconductor lasers are widely used in optical communications and many other applications today. These semiconductor lasers can be categorized by their device structure as either edge emitting or surface emitting. Surface emitting lasers (SEL) have many attractive characteristics. One type of SEL that is focused on in this paper is the vertical cavity surface emitting laser (VCSEL). The VCSEL´s vertical geometry enables on wafer testing and standard batch fabrication. In addition, the standard VCSEL has a good electrical to optical conversion efficiency as well as a good optical fiber coupling efficiency. However, for use in applications such as Fiber to the Premises (FTTP), high bandwidth data networks, through silicon chip to chip optical interconnections, and many other applications, the VCSEL´s emission wavelength range should be 1300 nm-1550 nm. This wavelength range is optimal for low attenuation. With the consolidation of many data centers, a need for higher transport data rates has surfaced. Many centers have begun upgrading its access and aggregation rates to 10 Gbps and 40 Gbps, respectively. For many, this upgrade will require a more cost effective optical link (cabling, transceiver, etc.). The most important component of the link is the transceiver. The problems with developing an optical transceiver for FTTP and data center applications are the high level of integration, cost effective packaging and burst-mode optical transmission technologies in the upstream link [1]. The typical transceiver emitter design includes an edge emitting laser. By replacing the edge emitting lasers with a long wavelength VCSEL, the packaging cost of the transceiver could be reduced. Figure 1 shows the difference in the packaging approaches. This paper presents the design and fabrication of a VCSEL based transceiver with a metal semiconductor metal (MSM) photodetector (PD).