## 1 Introduction
The laser is then directly modulated at a bit rate of 10 Gb/s, delivering an error-free back to back (B2B) transmission at a received optical power of -11 dBm. Furthermore, the same laser reported in [13] was subsequently directly modulated and used to transmit a 10 Gb/s signal over 50 km of SSMF [14]. Such long-distance transmission is achieved due to the reduction of the direct modulation induced frequency chirp by implementing OIL [15]. Chirp, in systems employing direct modulation, is considered as one of the main limiting factors both in terms of the spectral efficiency as well as transmission distance (due to the interplay between the chirp and the fiber dispersion). The design of the chip in [14] can be further improved by introducing additional, grating sections to the device. This would allow the lasing frequency of each laser to be tuned separately, thus providing much better control over the emission wavelength. Moreover, it provides more control over the power injected from the master laser, allowing for the optimization of the OIL, thus optimizing the overall performance of the integrated device. Furthermore, dividing each laser into two different sections gives the ability to control the bias of each section individually. This results in achieving accurate control over the Bragg condition (accurate overlap between the longitudinal mode of the FP laser and the Bragg mirror reflection), hence better compensation of cleaving facets error. In this paper, we present an Indium Phosphide (InP) PIC that comprises of four sections, with different cavity lengths, realized in a master-slave configuration. All the sections of the PIC are active and can be biased separately. The complexity of the device structure and the amount of combinations of biases for each section results in different regimes of operation. Hence, an extensive characterization of the device, under different bias conditions, is critical in order to comprehend the device behaviour. Thus, in this paper, we present a detailed analysis of the device performance, under several bias conditions. We first carry out a static characterization of the PIC-based transmitter The effect of injecting light from the master into the slave laser on vital transmitter parameters, such as linewidth and RIN, is presented. Subsequently, the dynamic characterization of the device, with and without injection from the master laser, is also presented and the enhancement of the PIC modulation bandwidth under OIL is shown. Finally, using the optimum operating conditions obtained from both static and dynamic characterizations, the performance of the PIC in a short reach network scenario is verified qualitatively and quantitatively through eye diagrams and BER as a function of the received optical power measurements. The paper is organized as follows: Section 2 includes a full description of the PIC design and the specifications of the different sections. Section 3 presents the results of the static characterisation of the device, while the dynamic characterisation of the PIC is shown in Section 4. This includes a comparative study (with and without OIL) of the frequency response, as well as the validation of the device performance in a 10.7 Gb/s directly modulated transmission system. Finally, conclusions are drawn in Section 5.