High brightness, index-guided parabolic bow-tie laser diodes

The category of devices of interest in the paper is that of high power semiconductor lasers that also have high brightness. However, to achieve simultaneously high output optical power and a ´good´ quality (narrow single-lobed) output beam from semiconductor lasers that can be fabricated relatively simply and cheaply, it is necessary to carefully design the cavity to control the output beam characteristics. The authors present the outcome of a systematic study on compact, index-guided semiconductor lasers of different geometry to show that with suitable design of the laser cavity it is possible to achieve the desired operational characteristics. In particular, the parabolic taper geometry has been found to be well-suited to achieve high brightness. Details of the specially designed high power semiconductor material used to fabricate the devices are also presented. The main advantage of the proposed compact devices is that the narrow output beam is achieved without the use of external lenses, thereby reducing the device cost for applications involving free-space propagation. Output powers in excess of 600 mW per facet have been measured from parabolic lasers (45% wall-plug efficiency) without catastrophic optical damage, at I = 1 A = 20I_th, with a full width at half maximum far field intensity profile of ∼2.5°.