# Lossless WDM PON Photonic Integrated Receivers Including SOAs
## 1 Introduction  
Technological innovations are continuously introducing novel applications that greatly influence the way humans interact, make decisions and conduct businesses. It is estimated that traffic from wireless devices will account for more than 63 percent of total IP traffic by 2021 [1]. These applications demand enhanced capacity, coverage, low latency and high quality of service (QoS) from wireless as well as optical access networks. Optical fiber distribution networks (ODN) in already installed passive optical access networks (PON) can be exploited to cope with diverse traffic demands originated from 5G mobile fronthaul, backhaul and large capacity short reach point to point links [2]. Designing low cost, low complexity and high capacity short reach PON access links using ODNs is a challenging task due to high link loss, particularly for optical network terminals (ONTs) at the customer premises. ONT transmitter complex modulation formats can provide higher capacity (>10 Gb/s) but keeping conventional non-return-to-zero (NRZ) modulation is a better option for low complexity and cost. However, conventional PIN-TIA receivers have low sensitivity, therefore power budget and highercapacity cannot be managed at the same time. Alternatively, receivers employing avalanche photodiodes (APD) and TIA have been demonstrated for 25 Gb/s TDM-PON links, but these kinds of APDs are not yet widely commercially available [3,4]. In this scenario, optical amplification becomes essential. Erbium doped fiber amplifiers (EDFA) at the optical line terminal (OLT) can amplify all downstream traffic, but integrated semiconductor optical amplifiers (SOAs) are a better choice at the ONTs due to having a smaller footprint despite relatively higher noise. Moreover, SOA-PIN/TIA receivers have a relatively large margin in terms of bandwidth improvement compared to APDs and can be realized at any telecom wavelength [5]. A recent study about the applicability of SOAs in PONs concluded that managing the optical power budget (\(>\)29 dB) for greater than 10 Gb/s PON such as 25 Gb/s and 50 Gb/s while using state-of-the-art low-cost components is challenging and will require pre/booster or both amplifiers [6]. Monolithic III-V photonic integrated pre-amplified optical receivers that integrate SOA and photodiodes [7,8] and TIA [9] have already been demonstrated for up to 40 Gb/s high speed PONs. Among the different photonic integration technologies, silicon photonics is particularly promising for ONT transceivers due to large scale integration capability, low cost, and reliability. Hybrid integration of SOA and mode locked laser in an eight channel WDM silicon photonic transceiver using edge coupling was recently reported in [10]. Nevertheless, hybrid integration of InP-based SOAs on silicon-on-insulator (SOI) substrates using flip-chip bonding [11,12] techniques poses additional challenges in the design of SOA devices, as it affects important parameters such as effective reflectivity, coupling efficiency, and gain ripples. Design of SOA devices combined in photonic integrated circuits (PICs) required precise numerical modeling and optimization of existing models. Several numerical models have been proposed for calculation/estimation of SOA parameters and operational behavior [13,14]. [PERSON] et al. [15] presented experimentally validated SOA numerical modeling techniques applicable to a wide range of SOA devices by using the transfer matrix method (TMM). In [16], they reported an optimized SOA model using the transmission line matrix (TLM) method to simulate light propagation through the active region of SOA. [PERSON] et al. described a theoretical model of the SOA time domain oscillation dynamics, used for the simulation of the oscillation dynamics in the SOA-based random laser [17]. A wideband steady-state model of a strained MQW-SOA has been described in [18], which uses an asymmetric broadening function in the material gain and additive spontaneous emission calculations.