## 1 Introduction  
The ever increasing demand for bandwidth hungry applications, such as ultra-high definition video streaming, high resolution online video gaming and cloud services, are placing intensive pressure on existing fiber optic communication networks [1]. This has led to a \"capacity crunch\", where the existing networks struggle to meet the required bandwidth imposed by these new services and applications. Amongst the different network segments, the short reach and data centre networks (DCNs) form the last mile of the optical network. They require innovative low cost and low power solutions to be able to respond to the ever-increasing bandwidth demand challenges. Photonic integration [2] provides a promising alternative to systems employing discrete components. By integrating multiple optical functionalities onto one chip, photonic integration can deliver cheaper, lower footprint, and lower power consumption solutions for optical networks. This can be a major advantage for DCNs, where compactness, cost, and power efficiency are critical [3]. Photonic integrated circuits (PICs) are built from many different materials, on custom manufacturing platforms. These include silicon (Si), silica (SiO2), lithium niobate (LiNbO3), silicon nitride (SiN), indium phosphide (InP), polymer, or glass [4]. PICs provide many attractive features, including smaller photonic dies, higher data rates, lower power consumption, lower cost per bit of data, and better reliability compared to legacy optics. Integrating multiple lasers in a single chip provides many advantages, such as the ability to achieve in-chip optical injection locking (OIL). OIL entails injecting light from a master laser into the cavity of a slave laser, thus transferring its frequency and phase to the slave laser [5]. The transfer of the spectral characteristics from a spectrally purer master to a slave laser allows the improvement of various characteristics of the slave laser, such as optical linewidth [6], relative intensity noise (RIN) [7], and mode partition noise (MPN) [8]. Furthermore, it can also enhance the laser modulation bandwidth [9] and resonance frequency [10]. Several studies have shown that the OIL can push the slave laser modulation bandwidth beyond the k-factor limit [11]. A discrete OIL setup comprises different passive and active optical components, such as circulators, polarization controllers, isolators, master, and slave lasers. Such a setup suffers from instabilities due to polarization dependence in case of usage of standard single mode fiber (SSMF). Use of polarization maintaining fiber (PMF) based components could avoid the polarization dependence issue. However, it still suffers from temperature variation in the injection path and introduce large insertion losses (due to the passive components used). An on-chip (integrated) OIL solution can provide the same advantages as a discrete OIL setup, whilst offering a simpler, cheaper, smaller footprint, and polarization independent operation. From the DCN and access network perspective, the ability to increase the modulation bandwidth of a laser is of particular interest, as it enables direct modulation of commercially available lasers with higher data rates. Direct modulation is a simple modulation technique, where the amplitude of the optical wave is modified, by varying the strength of the laser excitation [12]. It alleviates the requirement for bulky and lossy external modulators in the transmitter, thus providing a cost and energy-efficient solution for DCNs. The high sensitivity of DCNs to both cost and energy favours direct modulation as an electro-optic conversion technique. Previous work has shown that multiple lasers implemented in a single PIC in a master-slave configuration can be directly modulated and used as a transmitter in short reach networks. In [13], the authors report on a two-section discrete mode laser device in a master-slave configuration that achieves a side mode suppression ratio (SMSR) over 50 dB and a RIN of -142.6 dB/Hz.