Narrow spectral linewidth under wavelength tuning in thermally tunable super-structure-grating (SSG) DBR lasers

Narrow spectral linewidth characteristics are demonstrated in thermally wavelength tunable super-structure-grating distributed Bragg reflector (SSG-DBR) InGaAsP-InP lasers. SSG reflectors were fabricated with a multiple-phase-shift insertion method using electron-beam lithography. The phase distributions of the SSG´s were optimized to obtain uniform reflection peaks. Incorporating thin-film Pt heaters into the lasers enables us to tune the lasing wavelength by the thermal effect. The device has a wide quasi-continuous tuning range of 40 nm with CW operation at room temperature. The spectral linewidths, frequency fluctuations, and tuning speed in thermal wavelength tuning were studied compared with those in electrical tuning. Experimental results showed that thermal tuning does not influence frequency fluctuations and spectral linewidths, but the tuning speed was slow. Narrow spectral linewidths below 400 kHz were achieved in a wide quasi-continuous tuning range of 40 mm