GHz Self-Pulsation Multisection DFB

• Description

  One of the most promising approaches to realize an all-optical clock recovery is based on employing self-pulsating lasers. For practical applications, however, one should achieve reproducible self-pulsation with high extinction ratio at high (multi-GHz) frequencies. This can be accomplished using multisection DFB lasers, where both the keywords, "multisection" and "DFB", are of crucial importance. Multisection lasers exhibit self-pulsations due to instabilities induced by coupling between regions of saturable absorption and regions of high gain. The repetition rate of the emitted pulses can be controlled by varying the current, I. It is approximately proportional to 1/sqrt(I) [1]. Importantly, self-pulsations only occur at certain ratios of the carrier lifetimes and differential gains in the gain and absorber sections. In general, pulsations are only likely to occur when the carrier lifetime in the highly pumped gain sections is sufficiently longer than the carrier lifetime in the less pumped absorber sections [2]. Considerable technological efforts are necessary to satisfy this condition, and employing DFB sections is one of the most attractive approaches in this regard [3].

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• Typical Results

  The simplest example of such a device is a two-section DFB laser. The simulation setup is shown in Figure 1. It consists of two identical DFB sections with MQW active regions, each injected with its own source of current. In such a simple two-section device, the self-pulsation regime arises only in the narrow range of the injection currents; it is never observed, for instance, for equal currents [3]. As an example, injecting 130 mA into the first section and 60 mA into the second section, we obtain self-pulsations with a repetition rate of 1.25 GHz, as can be seen from the RF spectrum shown in Figure 2. The first peak defines here the frequency of self-pulsations, while the other peaks correspond to the higher-order harmonics. The output waveform in Figure 3 shows that the pulse widths are FWHM=200 ps and the period is T=800 ps. Corresponding temporal oscillations of the carrier density in the MQW and SCH regions of the DFB sections can be monitored as illustrated in Figure 4.

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• Further Information

  Keywords: Multisection Laser, Distributed Feedback Laser (DFB), Self-Pulsation, All-Optical Clock Recovery
  
  Similar demonstrations are available in VPIComponentMaker Photonic Circuits and on the VPIphotonics Forum.
  
  [1] P.E. Barnsley et al., IEEE Photon. Technol. Lett., Vol. 3, No. 10, 942-945 (1991)
  [2] M. Ueno and R. Lang, J. Appl. Phys., Vol. 58, No. 4, 1689-1692 (1985)
  [3] M. Möhrle et al, IEEE Photon. Technol. Lett., Vol. 4, No. 9, 976-978 (1992)

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