Single mode - Multimode - Multimode (SMm) fiber structure provides a simple and cost effective method for exciting a single radial mode in a multimode fiber (MMF). The structure can be effectively utilized in improving the capacity of high speed communication links employing MMFs. In this work, we study the effects of change in source wavelength on the excited single mode in the output MMF of an SMm structure. We show that the change in source wavelength deteriorates the single mode excitation of the output fiber. However, the same performance can be re-established by changing the length of the middle MMF. For small changes in the wavelength, we also give a simple formula to predict the required change in the length. © 2015 IEEE.