1.5μm, mode-hop-free full C-band wavelength tunable laser diode with a linewidth of 8 kHz and a RIN of -130 dB/Hz and its extension to the L-band.

We demonstrate a narrow-linewidth, low-intensity noise, widely wavelength-tunable LD for which we adopted a long external cavity configuration (ECLD) with a tunable optical filter. By employing a simultaneous tuning circuit between the optical filter and the Fabry-Perot mode caused by the external cavity, the oscillation wavelength was successfully tuned over the full C-band without mode hopping. The tunable optical filter bandwidth was 0.55 nm (1530~1570 nm). We achieved a linewidth of less than 8 kHz obtained with a delayed self-heterodyne method. On the other hand, the linewidth estimated from the white noise level of the optical frequency modulation noise power spectrum of the laser output was as narrow as 314 Hz. A relative intensity noise (RIN) below -130 dB/Hz was simultaneously achieved over the C-band range. With the same configuration except for an optical filter with a filter bandwidth of 0.6 nm for L-band operation (1570~1610 nm), we also realized a full L-band wavelength tunable ECLD with a linewidth of less than 7.7 kHz and a RIN of below -126 dB/Hz.