Emission behavior of distributed Bragg-reflector ridge waveguide lasers exposed to strong optical feedback

Abstract

In this work, the influence of strong optical feedback on the emission behavior of distributed Bragg-reflector ridge waveguide diode lasers emitting at 1120 nm with different cavity lengths and facet reflectivities is investigated. Based on measurements of the optical output power, central emission wavelength, and spectral emission width, the different diode laser types are compared while optical feedback up to − 8 d B is applied. The observed changes of the optical output power and emission wavelength as well as the occurrence of coherence collapse states give insight into the resistance against feedback of the different diode laser types.

Optical Feedback Generated by Tapered Amplifiers Emitting at 1120 nm

“…With the optical isolator and the beam splitter BS1 an effective isolation of the DBR-RWL of −45 dB is achieved. It has been shown in [8] that the used DBR-RWL is only affected by a power loss less than 10 % up to feedback levels of −25 dB. Thus, optical feedback up to +20 dB from the TPA is acceptable for this setup.…”

“…Although the output power of the TPA may raise only slowly for higher seed power levels the reduction of the relative power feedback ratio, which is the key influencing factor for the laser's feedback sensitivity, can be worth it. Second, even in the highly saturated regime the power feedback ratio is of the order of −15 dB requiring either a laser with extreme resistance against feedback [8], [19] or an optical isolator. Third, the occurrence of external feedback sources when using the MOPA has to be considered in detail.…”

“…The setup extension for the external feedback generation is comparable to the setup presented in [8]. As described there the reflection geometry with the lens L5 and the mirror M1 yields the highest coupling efficiency of the feedback back into the TPA.…”

“…The experimental setup for the experiments with the solitary MOPA configuration is shown in fig. 3 provided by a DBR-RWL with a length of 3 mm and a facet reflectivity of 30 % which is described in detail in [18], [8]. The laser emission is collimated by an aspherical lens L1 with a focal length of 8 mm and guided by mirrors through an optical isolator (OI) with an isolation of 40 dB.…”

“…4, 12489 Berlin, Germany TPA may deteriorate the spatial beam quality [6], [7] but it can be expected that the backward propagating light is also amplified in the TPA and increases the feedback towards the MO dramatically. With respect to the feedback sensitivity of master oscillators like DBR-RWLs [8] a proper selection of the laser and optical isolator is necessary.…”