Single-mode lasers at 1120 nm with electrical temperature-tuning of the internal grating
Fig. 1: DBR-RWL on C-mount with contact for DBR heaters
Fig. 2: Voltage, optical power and efficiency as a function of driving current of a DBR-RWL at 1120 nm
Fig. 3: Map of the spectral distribution of a DBR-RWL as a function of current through the DBR-heater section. Inset: sketch of the chip layout with DBR-heater (blue)
Laser sources emitting light at 560 nm can be used, for example, for time-resolved fluorescence and atomic spectroscopy, confocal microscopy, photocoagulation in ophthalmology, medical skin treatments, and high-resolution refractometry. However, for many applications in this field current laser sources lack direct modulation capability, suffer from low efficiency, and are usually fixed in their wavelength. Semiconductor-based laser sources, developed within the BMBF-funded Yellow project could be the solution to eliminate these restrictions. They are the basis for laser modules delivering the required performance parameters. Due to their compact size – they are only as big as a matchbox – they also enable mobile applications. With them, equipment becomes transportable, examinations can be executed in situ, and results are thus available much faster.
As direct-emitting laser diodes at 560 nm are currently not available, the FBH uses the concept of frequency doubling. The institute now developed monolithic distributed Bragg reflector ridge waveguide diode lasers (DBR-RWL) at 1120 nm featuring high optical output power, nearly diffraction limited beam, and narrow spectral linewidth [1]. These are the basis for future small-sized laser modules at 560 nm using second-harmonic generation (SHG).
The newly developed lasers feature highly strained InGaAs quantum wells and 5th order surface gratings for a stabilized emission wavelength around 1120 nm. Integration of a distributed Bragg reflector (DBR) into the rear part of an RW was in part adopted from previous DBR-RWL emitting at 1064 nm [2]. The challenge was to develop structures not exhibiting stable laser emission at 1120 nm as demonstrated earlier [3], but also allow to technologically implement DBR gratings. Furthermore, the new structure also comprises electrical heaters next to the DBR which enable a tuning of the emission wavelength.
The DBR-RWL achieved output powers up to 1 W and a maximum conversion efficiency of about 34% with a spatial and spectral single-mode emission. In a preliminary reliability test at 0.4 W a lifetime of more than 1,000 h could be demonstrated. Therefore, the laser sources should allow for an efficient non-linear frequency doubling to 560 nm in the near future.
Publications:
[1] K. Paschke, H. Wenzel, C. Fiebig, G. Blume, F. Bugge, J. Fricke, G. Erbert "High brightness, narrow bandwidth DBR diode lasers at 1120nm", IEEE Phot. Technol. Lett. (accepted 2013).
[2] K. Paschke, S. Spießberger, C. Kaspari, D. Feise, C. Fiebig, G. Blume, H. Wenzel, A. Wicht, G. Erbert, "High-power distributed Bragg reflector ridge-waveguide diode laser with very small spectral linewidth", Opt. Lett. vol. 35, no. 3, pp. 402-404 (2010).
[3] F. Bugge, G. Erbert, J. Fricke, S. Gramlich, R. Staske, H. Wenzel, U. Zeimer, and M. Weyers, "12 W continuous-wave diode lasers at 1120 nm with InGaAs quantum wells", Appl. Phys. Lett. vol. 79, no. 13, pp. 1965-1967 (2001).
FBH research: 14.06.2013