Proceedings - Viện Vật lý

_________________________________________________________________________________Advances in Optics, Photonics, Spectroscopy and Applications. Aug. 2006, Cantho, VietnamHIGH POWER 780 nm DFB LASERWITH 500 KHz LINEWIDTHT-P. Nguyen * , A. Klehr, O. Brox, G. Erbert, and G. TränkleFerdinand-Braun-Institut fuer Hoechstfrequenztechnik,Gustav-Kirchhoff-Straße 4, 12489 Berlin, GermanyWe present experimental investigations on high power ridge-waveguidedistributed feedback (DFB) lasers in the wavelength range around 780 nm with anoutput power of more than 200 mW in single lateral mode. The DFB lasers weregrown by low-pressure metal organic vapour phase epitaxy (MOVPE) andmounted p-side up in SOT headers. The threshold current is around 50 mA andthe slope efficiency is 0.7 W/A. The profile of the lateral far field has a FWHM of12° and reveals stable lasing of the fundamental lateral mode with low beamsteering up to 200 mW. The optical spectra show single mode emission with aside-mode suppression ratio of more than 50 dB. The linewidth of the lasers weremeasured with a heterodyne experimental setup. Linewidth as low as 500 kHzhave been measered. For the first time detailed investigations of the linewidth independence of optical power of 780 nm DFB laser are presented.Keywords: Semiconductor lasers, distributed-feedback lasers, high-power lasers,linewidth measurement.1. IntroductionNarrow-linewidth semiconductor lasers emitting in the wavelength rangebetween 760 and 790 nm are attractive for applications such as state selection inrubidium atomic clocks, Doppler laser cooling, nonlinear frequency conversion,Raman and absorption spectroscopy. These applications require a stable lasingfrequency together with a high output power.Fabry-Perot laser diodes combined with a grating in an external cavityconfiguration can satisfy these requirements. However, these hybrid devices areexpensive since mechanical and thermal stabilization schemes must be applied /1/.Another way to provide narrow linewidth high power lasers is the monolithicintegration of grating sections into the cavity. Either passive gratings (DBR lasers)or active grating (DFB lasers) can be applied. Since DBR lasers suffer from modehopping under modulation we focus herein on DFB lasers.It has been demonstrated that DFB lasers fabricated with a two-step growingprocess can reach a high output power of more than 100 mW /2/. Recently, RWDFB laser emitting 200 mW in a single lateral and longitudinal mode at an adjacentwavelength of 780 nm were presented /3, 4/. In /5/, the linewidth measurements*E-mail: nguyen@fbh-berlin.de267