In data centers, the multi-mode fiber (MMF) links and vertical cavity surface emitting laser (VCSEL) diode are widely used for short-reach optical communications (< 100 m) because of their low cost and their ability to handle the ever-increasing data rates. In conventional VCSEL drivers, the laser diode driver (LDD) can be bonded to a chip carrier, while the host chip is bonded to another chip carrier. This host chip contains an electrical link driver and is connected to the VCSEL driver via a short electrical link. To reduce the overall power consumption of the conventional VCSEL driver system, the electrical link driver in the host chip can be modified so that it can drive the VCSEL diode directly, eliminating the laser diode driver. Thus, the modified driver can drive either an electrical link or a VCSEL diode. By modifying the packaging, the VCSEL diode can be wire bonded to the host chip and directly driven. 
Driving a VCSEL diode requires features such as asymmetric equalization, relatively low modulation current, and DC current source to bias the VCSEL. On the other hand, driving an electrical link requires symmetric equalization, relatively high output voltage swing from the driver, and matched output impedance. Accordingly, a typical electrical link driver cannot drive a VCSEL diode and the VCSEL driver is not suitable for driving an electrical link. The proposed design is a single-ended source-series-terminated (SST) voltage-mode driver in a CMOS 65 nm technology with three driving modes: driving electrical links with losses up to 16 dB (mode I), driving VCSEL diodes through a short electrical link (mode II), and driving VCSEL diodes directly wire bonded to the driver (mode III). The proposed design provides a tunable output swing without changing the driver output impedance and achieves a smooth transition between symmetric and asymmetric equalization as needed. In simulation, the proposed triple-mode driver operates up to a bit rate of 20 Gb/s, and dissipates at most 27.6 mW of power when operating at mode II when using a supply voltage of 1.2 V.