Tunable multi-wavelength picosecond optical pulse generation using multiple optical path approach in a self-seeded gain-switched laser diode scheme

Tunable multi-wavelength picosecond optical pulse generation is of great interest for many applications such as high-bit-rate wavelength division multiplexing (WDM) communication systems and optical fiber sensors. A simple way to generate tunable picosecond optical pulses at arbitrary repetition rate is self-injection seeding of a gain-switched FP laser diode. In this scheme, a weak feedback of selected wavelength is introduced by the external cavity to the gain switched laser diode, resulting in the emission of single mode pulse trains, provided that the feedback arrives during the pulse build-up time. The wavelength of the output pulses is selected by the use of a wavelength selective element such as a grating in an external cavity or a dispersion shifted fiber. In order to obtain a multi-wavelength operation, a number of wavelength selective elements are generally required. In this work, a multiple optical path approach has been developed, the wavelengths of the picosecond optical pulses can be selected by the use of multiple optical paths in an external cavity containing only one wavelength selective element. By adjusting the wavelength selective element and the corresponding optical paths, the wavelengths and their spacing can be readily tuned. This approach is simple and of low cost, thus providing an attractive alternative to tunable multiwavelength picosecond optical pulse generation.