## 1 Introduction  
Reflective semiconductor amplifiers (RSOAs) are special version of semiconductor optical amplifiers (SOAs) constructed with an anti-reflective coating on the front facet and a high reflectivity coating on the rear end [1]. This design modification in the active medium cavity conveniently allows an optical signal coming from one (forward) direction to have its intensity increased and at the same time its information content altered as it exits from the other (backward) direction without using additional fiber hardware and fiber connections. The RSOAs downstream amplification and upstream modulation dual functionality together with their capability of providing higher gain with lower injection currents, less polarization dependency, higher modulation linearity, lower noise figure and less temperature sensitivity than their conventional counterparts [2, 3] has rendered these elements indispensable for the realization of modern access applications which critically rely on the manipulation of bidirectionally flowing data [4; 5; 6; 7; 8; 9; 10; 11; 12] and where wavelength-independent, i.e., color-less, operation is highly desired [13]. Still, the data rates that RSOAs can support in these applications are limited by the RSOAs slow direct (electrical) modulation speed, which in turn is constrained by RSOAs finite modulation bandwidth being as low as very few GHz according to evidence based on experimental measurements [14] and numerical simulations [15]. A promising solution, which owing to its clear concept, feasible implementation and passive nature has gained wide popularity across the research community, is to resort to frequency discrimination and equalization [16]. The idea is to properly tailor the spectrally broadened components of the data encoded signal at the RSOA output, which occur due to the dynamic modulation of the RSOA bias current and the subsequent perturbation of the RSOA gain. For this purpose, different optical notch filtering technologies, including a delay interferometer (DI) [17; 18], a fiber Bragg grating (FBG) [19], an array waveguide grating (AWG) [20] and a microring resonator [21], have been proposed. Recently, we employed a birefringent fiber loop (BFL), either alone [22], in cascade with another BFL [23] or assisted by an optical bandpass filter (OBPF) [24], to a standard SOA configured as intensity modulator. However, applying this scheme to an RSOA is not a trivial task due to the RSOA double-pass structure, which inherently imposes a greater strain on its dynamic behavior [12; 25], especially subject to a fast electrical excitation [26]. Thus in this paper, we experimentally demonstrate that using a BFL can significantly boost the direct modulation capability of an RSOA. Specifically, we verify that this enhancement can be achieved well over the RSOA nominal modulation bandwidth and up to a point which can satisfy at least the mid-term needs of the target applications RSOAs are destined to serve. To this end, the BFL proven potential to improve the RSOA direct modulation performance in combination with the BFL attractive features can favor the adoption of this passive module as an efficient and affordable alternative for enabling the unobstructed exploitation of RSOAs for intensity amplification and modulation purposes.