In this letter, we report the dynamics and performance of a 1.3-μm InAs/GaAs directly modulated quantum-dot laser (QDL) under strong feedback. At a direct modulation speed of 10 Gbps, error-free back-to-back operation of the QDL under a feedback level of −12 dB was realized. Feedback-resistant fiber transmission over 20 km under a maximum optical feedback level of −9 dB was also demonstrated with a power penalty of less than 1 dB at a bit error ratio (BER) of 10–3. The performance of the QDL was compared with directly modulated quantum-well laser (QWL) with similar parameters, showing a clear advantage in feedback resistance of QDL.

The reflection Airy distribution (RAD) of a Fabry-Pérot (F-P) resonator is deduced with the consideration of the mode coupling between the cavity resonance field and the initial back-reflected field at the input F-P resonator facet, as well as the influence of the loss/gain factor. A waveguide loss/gain measurement method is proposed based on the measurement of the finesse of the RAD, which is intrinsically free from the influence of the coupling loss and the substrate scattering noise. The waveguide loss can be measured with a simple single-facet coupling setup, considerably reducing the coupling difficulty and the complexity of the measurement system while achieving the same or better measurement accuracy as that of the transmission F-P method.

The optical feedback tolerance (OFT) of a distributed Bragg reflector (DBR) laser was investigated experimentally. The static and modulation performance of the DBR laser under optical feedback was examined by evaluating its relative intensity noise (RIN) and bit error rate (BER). It is shown that the OFT of the DBR laser is closely related to its peak wavelength detuning relative to the Bragg wavelength. A high tolerance to optical feedback was demonstrated, both in the continuous wave (CW) and the direct modulation (DM) states, when the DBR laser was red-detuned relative to the Bragg wavelength. The excess RIN induced by optical feedback was well suppressed to a level of −140 dB/Hz at a feedback level of −9 dB in the CW state. In a 10 Gbps direct modulation state, bit error rates (BER) below 1 × 10⁻⁹ and 3 × 10⁻⁷ were obtained under a feedback level of −15 dB and −9 dB, respectively, for the case of back-to-back transmission. After 20 km fiber transmission, the BER still maintained below 1 × 10⁻⁷ under a feedback level of −15 dB, with a power penalty of less than 1 dB.

Aiming to realize high-speed optical transmitters for isolator-free telecommunication systems, 1.3 μm p-modulation doped InGaAs/GaAs quantum dot (QD) lasers with a 400 μm long cavity have been reported. Compared with the un-doped QD laser as a reference, the p-doped QD laser emits at ground state, with an ultra-low threshold current and a high maximum output power. The p-doped QD laser also shows enhanced dynamic characteristics, with a 10 Gb/s large-signal direct modulation rate and a 7.8 GHz 3dB-bandwidth. In addition, the p-doped QD laser exhibits a strong coherent optical feedback resistance, which might be beyond −9 dB.

With the deployment of the fifth generation of mobile networks (5G), 25 and 100 Gb/s directly modulated lasers and modules will become the mainstream optical transmitters. A directly modulated InGaAlAs/InP distributed Bragg reflector (DBR) laser is fabricated by butt-joint technology. A 25 Gb/s data transmission over a single-mode fiber of up to 10 km is demonstrated, and a wavelength tuning range of 14.28 nm is achieved through injection current tuning of a DBR section and temperature control of a thermoelectric cooler (TEC), which is the best candidate of colorless light sources for wavelength-division-multiplexed passive optical network (WDM-PON) systems.