In metropolitan networks, one way to increase the data rates is to introduce Dense Wavelength Division Multiplexing (DWDM) in passive optical network (PON), with distances ranging from a couple of ten’s kilometers to several hundred kilometers, at data rates ranging from 1 to 10 Gb/s. A realistic implementation requires achromatic components, for which the provider can fix the operating wavelength in order to have the same type of components in the consumer’s home. These achromatic components must be low cost, which implies their ability to be directly modulated. It was recently shown [1] that self-seeded-reflective semiconductor optical amplifier (RSOA) could be the candidate. The RSOA is coupled to a Faraday mirror, which is located at a few kilometers in a central office, giving a Free Spectral Range of the extended cavity of the order of 100 kHz. Its wavelength is fixed on the “red” side of the transmission window of a 100 GHz-wide filter, as it is confirmed by our theoretical approach. It was shown [1] that a direct modulation at a few Gbits/s will stand BER (Bit Error Rate) compatible with the standard of optical telecommunication systems. A few descriptions of filtered optical feedback have been done [2, 3] in the literature. We use a Green Function approach, which enables us to describe the case of long delay and strong optical feedback-coupling (anti-reflection coating of the coupling face of the RSOA). In this communication, we focus particularly on the ability for the coupled device to switch on and off, which is essential for the system. The characteristics of the switch-on time is detailed for such a RSOA submitted to strong filtered optical feedback, using a Green function approach [3]. We discuss how such an RSOA coupled to a so long cavity is a low-cost component for WDM-PON operating at several Gbits/s.