Development of Novel Distributed Feedback Semiconductor Lasers with Reflection Insensitivity and Very Low Chirping Property

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1. Purely Gain-Coupled Distributed Feedback (DFB) Laser A novel DFB laser structure has been proposed, where pure gain coupling without index coupling is in principle brought about. We realized it by utilizing a special growth kinetics of organo-metallic vapor phase epitaxy, and achieved room-temperature continuous-wave operation with very low threshold current of 17mA. We have also showed theoretically and experimentally that, in the gain-coupled DFB laser, the oscillation mode is uniquely defined irrespective of facet phases, and there fore that very high single mode yield is obtainable even with as-cleaved end facets.2. External Reflection Insensitivity in Gain-Coupled DFB Lasers Dependence of intensity noise on external reflection of the above laser has been measured and compared with that of the conventional DFB laser. If the amount of reflection was less than 1%, the excess noise induced by the reflection was 10-20dB less in the case of remote reflection, and virtually no increas … More e in noise was observed in the case of adjacent reflection.3. Ultralow Chirping, Single Mode Optical Short Pulse Generation in Gain-Coupled DFB Lasers We have tried gain-switching short optical pulse generation experiment in the above laser using electrical pulses, and obtained an optical pulse of 16ps FWHM. Time-averaged spectra of the optical pulse have been measured and surprisingly found to be of single mode with 0.12nm FWHM. The linewidth enhancement factor estimated from these values is as small as 1.6.4. Low Chirping DFB Lasers with Distributed Electrode and Modulated Stripe Width Structures It has been shown through numerical simulation that, by using the above structures proposed here, the oscillation wavelength shift resulting from the longitudinal spatial hole burning can completely be eliminated, and that the chirping accompanying the relaxation oscillation can considerably be reduced.5. Monolithic Integration of a DFB Laser and a Modulator / Amplifier for Low Chirping Operation An alternative approach to realize low chirping modulation has been tried by integrating a traveling wave optical amplifier / modulator. We pointed out the usefulness of angled facets formed by reactive ion etching for reduction of optical cross-talk. The fabricated integrated device exhibited performances good enough for practical use, such as 20mA threshold and 10dB optical gain. Less