Effect of Optical Feedback on the Wavelength Tuning in DBR Lasers

Abstract

Optical feedback has an impact on the tunability of lasers. We created a model of a tunable distributed Bragg reflector (DBR) laser describing the effect of optical feedback from a constant reflector distance on the wavelength tuning. Theoretical and experimental results are in good agreement. A further discussion of the model sheds light on design rules to reduce the effect of optical feedback on the tuning behavior. We introduced a new parameter called mode loss difference (MLD) as a metric for the feedback tolerance of the tuning behavior. A large MLD indicates higher tolerance of the laser to cavity length variations.

Influence of Losses on the Laser Voltage Drop of the Active Section

“…In order to compare the measurements with calculations, we use the model of the tunable DBR laser from [9] to calculate the lasing wavelength. Subsequently, we follow the explanation derived in [8]: The wavelength dependent loss results in a wavelength dependent threshold gain, threshold carrier density, and gain voltage.…”

“…The Bragg grating reflectivity spectra can be calculated by the transfer matrix (Tmatrix) formalism [19,21]. Another helpful approach was described in [9]: the grating can be approximated by a normal distribution, only taking into account the main reflection peak and neglecting the satellite peaks. The reflectance coefficient rB and the transmission coefficient tB can be described as…”

“…To generalize the model, one can consider the presence of optical feedback from a reflection with reflectance coefficient r3 outside the laser cavity at a constant optical distance Lf. In order to describe this external cavity next to the laser cavity we can use the effective mirror model [19] which reduces the twocavity problem to a single cavity with an effective reflectivity [9] (…”

“…The mathematical model deriving this relationship from first principles of continues tuning of a laser under optical feedback is described by [8]. A related publication [9] describes the influence of optical Berlin, Germany (e-mail: david.felipe@hhi.fraunhofer.de).…”

“…The wavelength of each mode can be calculated by solving the condition for the round-trip phase [19]. Detailed descriptions of the wavelength calculation and mirror loss in tunable lasers are described in [8,9]. However, for certain feedback ratios the lasing mode emission line appears to be split and the lasing wavelength and associated mode are set by the smallest linewidth rather than the smallest mirror loss [20].…”