Technique to compensate waveform distortion in again-saturatedsemiconductor optical amplifier using a semiconductor saturable absorber

On the output characteristics of a semiconductor optical amplifier driven by an ultrafast optical time division multiplexing pulse train

“…Taking however into account the general rule-of-thumb which states that in an OTDM network designed to operate at a given frequency, the FWHM must be at least less than one third (1/3) of the duration of the assigned time slot in order to avoid undesirable crosstalk on the adjacent pulses [50] and by applying it at 10 GHz, we deduce that the FWHM cannot exceed approximately 33 ps. Returning now back to (36) and substituting this maximum permissible value of the FWHM, we find that the carrier lifetime must take values smaller than roughly 333 ps, which can be easily provided with the available SOA technology. By appropriately combining thus the involved parameters on the basis of the foregoing remarks, the chirp can be satisfactorily enhanced, as shown in the bottom part of Fig.…”

“…If these pulses are inserted in an optical transmission system, for example, then this shape distortion and broadening will add to the negative effects of the various propagation impairments, such as dispersion and attenuation, and make them more deleterious at the cost of increased power penalty [28] in order to obtain the same bit error rate and hence performance as with one pulse. Instead of deploying thus complex methods and techniques to compensate for the waveform distortion and restore the shape of the amplified pulses [34][35][36], it is only sufficient to keep the small signal gain below or close to 20 dB, which is a goal that can be easily achieved by simply decreasing the SOA bias current [33]. The satisfaction of this requirement is however undesirable for all-optical switching, which is an application on which we will particularly focus hereafter due to its special importance in the development of OTDM networks.…”

“…7. By taking now the limit T car ¼ 100 ps and placing it in (36), it can be calculated that the FWHM must be higher than 10 ps. Taking however into account the general rule-of-thumb which states that in an OTDM network designed to operate at a given frequency, the FWHM must be at least less than one third (1/3) of the duration of the assigned time slot in order to avoid undesirable crosstalk on the adjacent pulses [50] and by applying it at 10 GHz, we deduce that the FWHM cannot exceed approximately 33 ps.…”

Pattern effect reduction scheme for high-speed all-optical amplification system

“…13,14 The most important drawbacks are the pattern effect (PE) phenomenon and the output pulse's temporal and spectral distortion. 1,15 Several research works for removing PE have already been performed, such as electronic feedback, 16 using saturable absorber, 17,18 reduction of the carrier life time by injection of continuous wave light, 19,20 clamping of the gain by laser oscillation inside the device, 21,22 using an interferometric method, 23 an optical delay interferometer, 24 using holding light injection, 25 using an asymmetrical Mach-Zehnder interferometer, 26 and using a birefringent fiber loop mirror. 27 However, these methods did not represent a completely satisfactory solution for these issues.…”

Noise and Regeneration in Semiconductor Waveguides With Saturable Gain and Absorption

“…The basic idea of the device is to use the gain saturation in the SOA combined with the absorption bleaching in the EA to achieve a simple and potentially cheap device with regenerative properties. This type of device, with a single amplifier-absorber pair, has been proposed earlier for regeneration [6], but also for chirp control in modulators [7] and compensation of waveform distortion in SOAs [8]. The addition of the EA to the SOA can thus potentially remedy some of the shortcomings of the SOA by sacrificing some gain of the device.…”