Performance analysis and improvement of semiconductor optical amplifier direct modulation with assistance of microring resonator notch filter

Theoretical Analysis of Directly Modulated Reflective Semiconductor Optical Amplifier Performance Enhancement by Microring Resonator-Based Notch Filtering

“…This fact confirms that the RSOA modulation response exhibits a low-pass characteristic, which is in agreement with the same trend noticed from extensive numerical calculations [49]. For the MRR, on the other hand, the modulation response is [24] T…”

“…For this purpose we investigated the impact of the parameters associated with the optical and electrical RSOA excitation signal on the error probability (EP) which, for acceptable performance, should not exceed the forward error correction (FEC) threshold of 3.8 × 10 −3 [22,24]. The error probability is analytically extracted through the Q-factor, which is defined as…”

“…According to this fact, the continuous increase of the examined parameter values would seem natural for supporting faster RSOA direct modulation. However, there are physical limitations in this trend, which are imposed by the RSOA CW gain and the maximum amplitude difference, that is, extinction, between marks and spaces, AD 1/0,max [24]. In fact, increasing too much the CW power forces the RSOA to enter into the deep saturation regime where it provides a reduced optical gain, while increasing too much the bias current shifts the RSOA electrical modulation to occur beyond the linear gain-current region, that is, into the hard limit where the information-driving current is made to experience an almost flat RSOA optical gain [58].…”

“…Figure 7 compiles the encoded pulse waveforms, chirp and pseudo-eye diagrams (PEDs) for favorable (top) and adverse (bottom) RSOA direct modulation which occur at 3 Gb/s and 5 Gb/s, respectively. These opposing cases can be quantitatively compared not only against the EP but also against the maximum amplitude difference between marks, AD 1,max , and AD 1/0,max [24], red chirp fluctuations (CF) [59] and PED eye opening (EO) [24]. Thus, EP = 4.3 × 10 −3 at 3 Gb/s vs. 7.6 × 10 −2 at 5 Gb/s, AD 1,max = 0.22 dB at 3 Gb/s vs. 1.03 dB at 5 Gb/s, AD 1/0,max = 10.02 dB at 3 Gb/s vs. 8.1 dB at 5 Gb/s, CF = 2% at 3 Gb/s vs. 15% at 5 Gb/s and EO = 87% at 3 Gb/s vs. 72% at 5 Gb/s.…”

“…Thus, different schemes that act as optical notch filters on RSOA-encoded outputs have been reported, such as the delay interferometer (DI) [17,18], the fiber Bragg grating (FBG) [19] and the arrayed waveguide grating (AWG) [20]. In the same technological category also fall schemes that have been applied on conventional directly modulated SOAs, such as the birefringent fiber loop (BFL), either alone [21], in cascade with another BFL [22] or assisted by an optical bandpass filter [23]; and the microring resonator (MRR) [24]. The MRR is a special form of powerful waveguides [25,26], and exhibits distinctive characteristics over the aforementioned types of employed filters.…”