To obtain an optical triangular wave generator in which a rectangular optical pulse signal can be converted into a triangular wave in order to obtain a short output pulse width by employing an optical element causing chirp phenomenon due to the nonlinearity, and a band-pass filter.

An optical band-pass filter BPF 23 has a central wavelength within the chirp range of an optical element 22 and receives an optical output therefrom to produce a triangular optical pulse signal. The optical element 22 employs a single mode optical fiber and generates chirping through self phase modulation due to optical Kerr effect. The optical frequency is down- shifted during first half period of pulse but up-shifted during second half period and finally up-chirped to widen the pulse width and spectral width. Subsequently, it is passed through the BPF 23 to attenuate the spread spectra part, i.e. the head and tail parts of optical pulse signal, thus producing a triangular wave.