Fig. 1. Schematic view of the tunable DBR laser.

Fig. 2. Optical image of the packaged laser.

Fig. 3. Light-current characteristic of the InGaAlAs DBR lasers at 25°C.

Fig. 4. S21 curve of the InGaAlAs DBR laser at 25°C when the gain section, phase section, and DBR section were biased at 100, 0, and 0 mA, respectively.

Fig. 5. Wavelength tuning properties of InGaAlAs DBR lasers at 25°C.

Fig. 6. Typical optical spectra obtained from the InGaAlAs DBR lasers at 25°C.

Fig. 7. Experimental setup used to measure the PAM-4 transmission characteristics of the tunable DBR laser.

Fig. 8. PAM-4 eye diagrams of tunable DBR laser for BTB, 10 km, and 20 km transmission when the tuned wavelength is (a) 1559.8 nm, (b) 1555.7 nm, (c) 1552.4 nm, and (d) 1548.3 nm.

Fig. 9. 20 Gb/s PAM-4 BER performance of tunable DBR laser for BTB, 10 km, and 20 km transmission when the tuned wavelength is 1559.8 nm.