Emission wavelength stabilization in broad area lasers coupled to fiber Bragg gratings

摘要

Coupling to the fiber Bragg grating (FBG) is a well-established technique of emission wavelength stabilization in single mode pump lasers used for instance in Er-doped fiber amplifiers (see e.g. Ref. 1). The output power of these devices usually does not exceed 1 W due to limited heat transfer from narrow active stripe of the single mode laser diode. To satisfy increasing demand for wavelength-stabilized pump lasers with higher output power we attempted to extend FBG stabilization scheme to high power multimode broad area lasers. This scheme brings usual advantages of FBG stabilization such as environmental wavelength stability, compactness and low cost. Development work has been carried out using our reliable high power pump laser with output aperture of ～ 50 -100 μm. The emission wavelength of the free running laser was around 960 nm at room temperature. The fiber gratings with reflection maximum at about 975 nm were written in a commercially available multimode fiber. In initial experiments the laser was coupled with discrete optics to the multimode fiber containing FBG. Introduction of the spectrally selective optical feedback locked the laser emission to the Bragg wavelength. The laser emission remained locked to this wavelength up to a maximum drive current of 8 A within a heat sink temperature range of 40℃ in this experiment. The overall spectral width of stabilized laser emission facilitates effective and stable pumping into absorption lines as narrow as 5 nm FWHM. Similar results were obtained on the Bookham commercial pump modules with FBG in the output fiber. The modules emitted up 4 W of wavelength-stabilized power from the output fiber with 50 μm core diameter.