Abstract
The feasibility of employing a birefringent fiber loop to enhance the performance of a directly modulated reflective semiconductor optical amplifier is experimentally demonstrated for the first time. The birefringent fiber loop acts as an optical filter of opposite slope than that of the reflective semiconductor optical amplifier electro-optical response and counteracts the finite reflective semiconductor optical amplifier modulation bandwidth of only 0.89 GHz. By proper adjustment of its detuning, the birefringent fiber loop tailors the spectral components that physically manifest due to the reflective semiconductor optical amplifier dynamic perturbation subject to direct modulation in the saturated gain regime, and suppresses the pattern-dependent distortions in the time domain. In this manner, the birefringent fiber loop manages to significantly improve the quality characteristics of the encoded signal at higher data rates than those enabled by the reflective semiconductor optical amplifier limited modulation capability. Owing to the birefringent fiber loop, the reflective semiconductor optical amplifier modulation range is extended to 4 Gb/s at the raw bit error rate of 1.0×10−9, and to 11 Gb/s at the forward error correction limit of 3.8×10−3. These results, which are unique against the evaluation criterion adopted in the first case, and the modulation speed achieved with post-filtering schemes in the second, highlight the beneficial role that the birefringent fiber loop can play in supporting reflective semiconductor optical amplifier operation for intensity amplification and modulation purposes.
Highlights
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]
The data rates that RSOAs can support in these applications are limited by the RSOAs slow direct 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]
Since the birefringent fiber loop (BFL) filtering efficiency is critically determined by the detuning [23], ∆λ, which is defined as the difference between the continuous wave (CW) seeding wavelength and the wavelength of the nearest notch in the BFL response, we investigated the impact of this parameter on the operation of the scheme by assessing first the performance against the error probability (EP)
Summary
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]. 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]. 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
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