A DFB Laser With Integrated Passive Region Suitable for PAM-4 Modulation Signal

Numerous studies have shown that the use of PAM-4 modulation format for DFB lasers with integrated passive regions (DFB IPE lasers) can greatly improve information transmission capabilities. In this paper, it is found by theoretical analysis that a passive waveguide can reduce the photon concentration and injection current in the cavity under the same output optical power. The DFB IPE laser has large saturated optical power and slope efficiency, which reduces the distortion of the electro-optical conversion of the PAM-4 signal. A DFB IPE laser was fabricated with a total cavity length and passive waveguide length of 130 um and 40 um, respectively. The saturation output power, slope efficiency, and modulation bandwidth of this laser are 23.5 mW (61 mA), 0.41 W/A, 22 GHz, respectively. The relative intensity noise is also below −145 dB/Hz. Besides, we have verified the high temperature working capability of this laser in a 40 Gbps PAM-4 signal back-to-back (BTB) transmission system. When the signal peak-to-peak voltage is 750 mV, a clear eye diagram with an eye height of 196 mV is obtained at 343 K.