FBH research: 06.05.2020

Extended lifetime for DBR tapered diode lasers due to a novel internal output DBR-grating

The two main causes for blindness worldwide are diabetic retinopathy and age-related macular degeneration. These eye diseases can be treated by laser coagulation, a surgical therapy method for the thermal denaturation of tissue. Laser emission at 532 nm is widely used for such treatment. For this purpose, the FBH is developing diode lasers emitting at 1064 nm for second harmonic generation, thus halving the wavelength. FBH’s developments target high spectral radiance laser sources at 1064 nm as the basis for miniaturized green-emitting laser modules for laser coagulation.

Distributed Bragg reflector tapered diode lasers (DBR-TPL) are highly efficient and narrowband light sources – and therefore very well suited for this application. We demonstrated that DBR-TPLs are able to deliver an optical output power of more than 8 W. However, such high power levels limit the lifetime of DBR-TPL at 1064 nm to 2,400 h at the most. We have therefore developed DBR-TPL with an additional internal DBR-grating at the output side of the tapered amplifier section (a) in addition to DBR-TPL with standard facet coating (b).

These novel DBR-DBR-TPL showed similar electro-optical results with a small influence of the length of the front DBR-grating (see Fig. 2) compared to standard DBR-TPL.

The spectral emission is longitudinal single mode featuring a width of below 20 pm. This allows matching the spectral acceptance bandwidth of non-linear crystals. The quality of the emitted beam at 8 W is very good with more than 75% of the total output power in the central lobe, which is sufficient for efficient second harmonic generation. Furthermore, the low vertical far field of 15° (FWHM) enables simplified micro integration.

The lifetime could be doubled to 4,600 h by choosing the longest front DBR-grating with LfDBR = 20 μm, coming closer to the desired lifetime of 10,000 h for integration into miniaturized modules for laser coagulation. Therefore, the extended lifetime could be achieved without modifying the epitaxial structure. Moreover, the time and effort required for frontend processing remained the same.

Publication

[1] D. Feise, D. Jedrzejczyk, D. Krug, N. Werner, F. Bugge, A. Maaßdorf, R.-St. Unger, P. Ressel, K. Paschke, "High spectral radiance distributed Bragg reflector tapered diode lasers at 1060 nm with novel internal output DBR-grating", Proc. SPIE 10939, Novel In-Plane Semiconductor Lasers XVIII, Photonics West, San Francisco, USA, Feb 1-6, 109391F (2019).