We examine several critical issues related to laser diodes with wavelength λ approximately 750 - 1000 μm for WDM applications. Particular attention was given to the Vertical Cavity Surface Emitting Laser and Distributed Feedback Laser which are the most central components for the optical interconnect or local-area network, or for pumping the Er or Pr doped optical fiber. Regrowth control, stability and reliability at high power and high temperature operation as well as the optimal design are the most critical issues for the devices. Aluminum-free InGaAsP/GaAs is proposed as an alternative to AlGaAS/GaAs for the WDM applications. Perspectives are presented on how those problems especially, reliability and regrowth issues for WDM application can be eased by this material system.