Optical EngineeringNovel self-consistent method for determining optical coupling coefficients and grating losses of distributed Bragg reflector lasers
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Based on the stopband width measurement, the coupling coefficient of distributed feedback (DFB) lasers can be estimated with reasonably good accuracy. However, to characterize distributed Bragg reflector (DBR) lasers, many researchers have used the calculated coupling coefficient, since the stopband width from the reflectivity profile of the lasers is more difficult to clarify for this estimation compared to that of DFB lasers. It is especially true when grating losses due to scattering and absorption are large and difficult to measure for the surface grating devices. In this case, estimation of the coupling coefficient becomes more problematic or even erroneous. This work uses a novel method that involves implementing the relationship between the real and effective grating lengths and mode spacing under the subthreshold to determine the coupling coefficient and grating losses of DBR lasers. Through a self-consistent approach, for DBR lasers with a geometry of La =420 ?m and Lg=380 ?m, where La and Lg are the active-section and grating-section lengths, respectively, a coupling coefficient of 45 cm21 and grating losses of 38 cm-1 at the lasing wavelength of 833 nm were estimated with relatively low uncertainty of 10%.