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Dense wavelength division multiplexing at high data rate is believed to be a viable solution to the growing demand for large bandwidth optical communication. Such development requires a wide range of active and passive optical components. Semiconductor laser with high power and diffraction-limited output beam are important light sources for a number of applications including pump source for EDFA and Raman amplifiers, as well as free space optical communications. One of the most promising designs to obtain high brightness lasers is the so-called tapered cavity laser, which consists of a ridge and a tapered gain section [1]. In order to achieve single mode with circular emission, we developed curved grating coupled surface-emitting tapered lasers [2]. Figure 1 shows a schematic view of our laser. The lasers were fabricated on a strained InGaAs/GaAs/A1GaAs triple-quantum well GRINSCH structure. The 3-jim wide ridge is designed to only support the fundamental lateral mode. The ridge length is 400-jim. The function of the spoiling groove is to prevent any feedback from the tapered section to the unpumped region in the ridge side. Therefore the ridge and spoiling grooves promote fundamental mode operation and suppress high order lateral modes. Connected to the ridge is the tapered section, which provides most part of the gain needed for lasing. The length of the tapered section is 1 800-jim with a full angle of about 7 degrees, which is designed to accommodate the free diffraction of the beam inside the tapered section. The feedback mirrors consist of a cleaved facet on the ridge side and a curved second-order Bragg grating on the tapered side. The curvature of the grating is designed to approximately match the phase front of the forward propagating beam, in this case, the center of curvature is located at 1800 jim from the tapered end. This will make the output beam to be collimated and has a small divergence angle.
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