External cavity tunable laser with 25GHz frequency interval

The invention relates to an external cavity tunable laser with 25 GHz frequency interval. The laser comprise a laser cavity end mirror directly plated on a laser gain medium, and the laser gain medium, an intracavity collimating lens, an active optical phase modulator, a tunable acousto-optic filter and an intracavity total reflection mirror all arranged inside a laser cavity sequentially. The laser further comprises: an active polarization rotator arranged on the opposite side of the tunable acousto-optic filter from the intracavity total reflection mirror, a polarization beam splitter arranged behind the active polarization rotator, a first etalon, a first total reflection mirror, a second etalon, a second total reflection mirror, a drive source for the tunable acousto-optic filter, a pumping source for the laser gain medium, a drive source for the active optical phase modulator, a drive source for the active polarization rotator and a laser drive control circuit. The invention is compact with high performance, low cost for volume production and installation, achieves high spectral density, narrow spectral bandwidth and stable tunable laser output within a wide spectrum range.