The operation of a passively mode-locked erbium-doped fiber ring laser in two-wavelength pulse mode has been experimentally demonstrated.Multiple wavelengths can simultaneously oscillate owing to the wavelength-dependent transmission induced by birefringence.Due to additional polarization dependent cavity loss imposed by polarization dependent isolator,two-wavelength mode-locked pulses can be obtained.The wavelengths of two-wavelength mode-locked pulses can be switched among three wavelength bands.Furthermo...