Narrow bandwidth red emitting diode lasers
Narrow bandwidth diode lasers emitting in the red spectral range will be an alternative for commonly used He-Ne-Lasers in metrology and Raman spectroscopy in the future. Furthermore, such kinds of lasers enable high brightness red-emitting light sources for entertainment and display technology by wavelength multiplexing. Scientists from the FBH just recently succeeded to integrate distributed-Bragg-reflector (DBR) surface gratings in waveguide structures for diode laser emitting in wavelength range 630 nm…640 nm. Monolithic integration makes such laser sources very compact and stable.
For that purpose, FBH used a waveguide structure containing a p-side AlGaAs cladding instead of the typically used AlInGaP cladding layer. Such a structure enables an easier production of surface gratings using dry etching technology. FBH developed red-emitting ridge-waveguide (RW) diode lasers with 10th order (about 1000 nm period) surface gratings as wavelength selective reflector by using standard i-line stepper lithography. Such technology is very reproducible and paves the way to mass production.
First results turned out very promising: The new DBR-RWLs emit up to almost 100 mW optical output power in the wavelength range between 630 nm and 640 nm (Fig. 1). A grating period of 972 nm, for example, resulted in an emission of 635.35 nm (Fig. 2). The emission is spectrally narrow with less than 9 pm bandwidth and a side mode suppression ratio in excess of 18 dB. With customized coating a small linewidth necessary for high precision metrology and a higher side mode suppression ratio was achieved. A very simple and, at the same time, fast wavelength tuning can be performed by current modulation. Research on tapered laser structures with such monolithic integrated Bragg reflectors will lead to an output power above 100 mW with narrow spectral bandwidth in future.
D. Feise, W. John, F. Bugge, G. Blume, T. Hassoun, J. Fricke, K. Paschke, G. Erbert, "96 mW longitudinal single mode red-emitting distributed Bragg reflector ridge waveguide laser with tenth order surface gratings", Opt. Lett., vol. 37, no 9, pp. 1532-1534 (2012).