174-nm mode spacing in dual-wavelength semiconductor laser using nonidentical InGaAsP quantum wells

A very wide tuning range of dual-wavelength semiconductor lasers with properly designed nonidentical InGaAsP quantum wells is reported. As the external cavity of reflected-type grating telescope configuration is well aligned, the dual-wavelength operation can be achieved with a record wavelength separation as large as 174 nm (25 THz). The wide separation of two wavelengths is possible due to a proper modification of the external-cavity configuration and reduced gain competition of laser modes.