Theoretical analysis of pattern effect suppression in semiconductor optical amplifier utilizing optical delay interferometer

Semiconductor optical amplifier pattern effect suppression using Lyot filter

“…With the use of the Lyot filter, the pattern effect can be alleviated, as is evident in Fig. 2c where the peak variations of the '1's are balanced and the AM is restored to an acceptable value of 0.35 dB [10] while the eye diagram again becomes clear and open, having an ER of 17 dB. These improvements can be explained from the results in the frequency domain, which are shown in Fig.…”

“…2b. In fact, the marks suffer from severe amplitude fluctuations depending on whether they are preceded either by one or more spaces or other marks, as theoretically predicted in [10], resulting in an AM of 1.7 dB. Moreover, the eye diagram is degraded, since its shape is asymmetric, in accordance to [3] and comprises of sub-envelopes with its ER reduced below 10 dB.…”

“…2a. The logical '1's have an amplitude modulation (AM) of 0.35 dB [10], while the corresponding eye diagram in the right column has an extinction ratio (ER) of 20 dB. After the SOA alone, however, these features are not maintained owing to the pronounced pattern effect, which results in a poor performance observed in Fig.…”

“…However, this is not a fundamental problem but rather a technical difficulty that can be overcome with the commercially available technology, such as specialised PM photonic crystal fibres [11], which can enhance the stability of the scheme by making it less sensitive to changes in the environmental conditions. In comparison, there are other comb filter implementations with delay interferometers which are more robust to environmental perturbations, such as the birefringent fibre loop (BFL) [12] and the optical delay interferometer (ODI) [10]. The latter is also more compact and can be co-packaged with the SOA in a single module, which is more difficult to be done with the Lyot filter owing to its large physical size.…”

Semiconductor optical amplifier pattern effect suppression for return-to-zero data using an optical delay interferometer

“…In some practical applications, the return-to-zero ͑RZ͒ format is preferable in terms of receiver sensitivity and transmission performance. 10 In this case, the nature of the pattern effect phenomenon is different because it incurs fluctuations between the peakamplitudes of the data pulses 11 instead of overshoots at their leading edges. [7][8][9] Its impact on the pulses is also more severe, because by definition their duration is shorter than the bit period, which in turn imposes a greater strain on the SOA gain dynamics.…”