## 1 Introduction  
As multicore systems-on-chips (SoCs) have become mainstream as chips suffer from diminishing returns of miniaturization and the power wall, a new high-performance on-chip network architecture is needed to overcome the physical limitations of metal interconnects [1; 2]. A hybrid optical network-on-chip (HONoC) in which the electrical and optical layers are combined, using silicon photonics technology, is emerging as a new alternative for replacing metallic interconnects [3]. The HONoC uses the optical layer to transmit massive data and uses the electrical layer to send control packets or small-size data. As the number of cores in the system increases, the network-size-scalable architecture is highly desirable. The widely-known mesh topology is chosen due to its simplicity and regularity in terms of layout, after considering the advantages of the topology revealed by existing studies on mesh-based HONoCs [4; 5; 6].  
For reliable communication, the optical signal power arriving at the receiver should be higher than the sensitivity of the photodetector. Because of the significant insertion loss in large-scale HONoCs due to the accumulated microring resonator (MR) drops and waveguide crossings, the laser source output power should be increased. As the laser source is the most power-consuming device among the optical devices, the insertion loss acts as a dominant factor for the overall power consumption of the HONoC.  
[PERSON] et al. [7] suggested the dynamic laser power control to reduce the power consumption of the ONoC. However, adaptive laser power management demands complicated control and exhibits limited power efficiency. Moreover, even if the power efficiency of the chip is increased by reducing the laser source power, reliable communication is not guaranteed under high crosstalk noise environments with heavy data traffic cases [8].  
We propose a low-power scalable HONoC architecture by deploying semiconductor optical amplifiers (SOAs) and the closely related SOA placement algorithm considering the insertion loss and crosstalk noise change caused by SOA deployment. An analytic worst-case crosstalk noise model is developed to find the optimized SOA gain that minimizes crosstalk noise and to investigate the effect of SOAs on worst-case signal-to-noise ratio (SNR) in HONoC. Considering the relationship between SOA placement and worst-case insertion loss, we calculate the minimum SOA gain for laser source power savings.  
The remainder of this paper is organized as follows. Section 2 briefly provides related research and background information regarding insertion loss and crosstalk noise. In Section 3, we introduce the optical router and the SOA model and present a constraint optimization problem for implementing an SOA-enabled HONoC. In Section 4, to solve the constraint optimization problem, we propose an SOA placement algorithm and analyse the worst-case crosstalk noise. Based on the crosstalk noise model, the correlation between the SOA and the SNR is analysed. We also calculate the minimum SOA gain to apply laser source power independent of the longest path. In Section 5, we evaluate and compare the worst-case SNR and power consumption of SOA-enabled HONoC. We draw the conclusion in Section 6.