Designed for use in laboratory applications or for test and measurement of 25-Gbit/s datacom devices, the Model 1784 is an 850-nm, 25-Gbit/s, directly modulated, multimode vertical-cavity surface-emitting laser (VCSEL). The Model 1784 uses high-performance microwave circuitry to ensure clean delivery of the electrical input to the VCSEL chip, and the VCSEL's 50-µm output fiber enables the use of either 50-µm or 62.5-µm fiber. The AC-coupled input and internal bias circuitry allows connection to any high-speed 50-Ω SMA-compatible signal source without the need for additional bias circuitry. A 10-position switch allows for optimization of the VCSEL bias for different datacom applications.