## 1 Introduction  
The explosive growth of both fixed and mobile data-centric traffic along with the inevitable trend towards all-IP/Ethernet transport protocols and packet switched networks will ultimately lead to an all-packet-based converged fixed mobile optical transport network from the core to the access network. To address the increasing capacity and speed requirements in the access networks, wavelength-division multiplexed (WDM) and/or coarse WDM (CWDM)-based passive optical networks (PONs) are expected to emerge as the next-generation optical access infrastructure. However, due to several techno-economic hurdles, CWDM-PONs are still considered an expensive solution and have not yet made any significant inroads into the current access area. One of the key technology hurdles is the scalability of the CWDM-based PONs. Passive component optical insertion losses limit the reach of the network or the number of served optical network units (ONUs). The CWDM standard from the International Telecommunication Union-Telecommunication Standardization body (ITU-T G.694.2) defines a maximum of 18 channels operating over the entire optical fiber communication spectrum from 1270 nm to 1610 nm (e.g., 340-nm bandwidth) with 20-nm channel spacing [1]. In recent years, optically amplified CWDM approaches have emerged, and new designs of optical amplifiers have been proposed and demonstrated. The critical design parameter for these amplifiers is the very wide optical amplification bandwidth (e.g., 340 nm combined for both downstream (DS) and upstream (US) traffic directions). Recently, a hybrid Semiconductor Optical Amplifier (SOA)-Raman amplifier was shown to be capable of providing a 150-nm bidirectional gain (e.g., 75 nm in each direction separately) over the PON's downstream (1483-1557 nm) and upstream (1283-1357 nm) CWDM wavelength band with an 18 dB gain (\(<\)2 dB ripple) and 19.5 dB gain (1 dB ripple), respectively [2; 3]. Other researchers have proposed and demonstrated alternative designs to achieve wide amplifier gain bandwidths. For example, [PERSON] _et al._, demonstrated a discrete Raman amplifier with 100-nm gain bandwidth over the full O-band, but at the expense of six pumps, to obtain an average gain of 10.5 dB with less than 1-dB variations [4]. A fiber optical amplifier combining optical parametric and Raman processes was demonstrated by overlapping the parametric gain with pump-induced Raman gain in [5]. This approach was mainly focused on the influence of the pump-induced Raman gain on a broadband fiber optical parametric amplifier (OPA), without focusing on the optimization of the two processes and has exhibited a very high gain ripple. It exhibited a 208-nm bandwidth and a gain in excess of 10 dB; however, a very high gain ripple of \(\sim\)12 dB [5] made it inappropriate for network-type applications; furthermore, the effect of the generation of multiple idler wavelengths from the parametric process was not addressed. Recently, we presented the results for a 170-nm bandwidth HROPA with \(<\)4 dB gain ripple and minimum gain of 20 dB using only three pumps operating only at the upper band (e.g., 1450 nm-1610 nm) of the CWDM wavelengths [6; 7; 8]. In this paper, we extend our previous work to the lower half of the CDWM band (e.g., 1270 nm-1430 nm), which adds some challenges in the design. These challenges include the much wider operation frequency bandwidth of the hybrid Raman-OPA (HROPA) in the lower CWDM band compared to that of the upper CWDM band. In particular, although the wavelength range of the two bands (e.g., 1270 nm-1430 nm and 1450 nm-1610 nm) is the same (e.g., 160 nm), in the frequency domain, the lower CWDM band has a bandwidth of ~26 THz, whereas the upper CWDM band has ~20 THz. Hence, this much wider frequency bandwidth makes the selection of pump wavelengths and powers more challenging, in particular when high gain, low gain ripple and ultra-wide bandwidth is required.