Study on Bragg reflection waveguide diode laser

High power diode lasers are widely used for pumping of solid state lasers and fiber lasers, material processing, medical treatment, sensors, free-space optical communication, security and defense. However, the conventional diode lasers usually suffer from a large far-field divergence and strongly elliptical beam, which limit the direct applications. To improve the divergence, diode lasers based on Bragg reflection waveguide(BRW) are studied in this project, which utilizes the photonic bandgap(PBG) effect rather than the total internal reflection(TIR) to provide optical confinement. Several kinds of BRW lasers(BRLs) with different structures are designed and fabricated. First, the mode dispersion equation of the BRW is solved by the transfer matrix method and Bloch theory. The further analysis shows that the far-field distribution of BRW is determined by the mode shape in the cavity. In the case of Bragg form of PBG guidance, the optical field characteristics of a quarter-wave BRL and a single-sided BRL are studied. The essential reason affecting the far-field distribution is investigated. Finally, a twin-beam laser based on BRW is designed and demonstrated. Almost all the emission power of this laser is concentrated in two near-circular lobes in the vertical direction. The full-width at half maximum(FWHM) divergence angles of one beam are as narrow as 7.2° and 5.4° respectively in the vertical and lateral direction. Furthermore, the high brightness BRL with a ultra-narrow circular output beam is demonstrated by controlling the defect layer. The ultra-low vertical divergence of 9.8° with 95% power content and 4.9° with the FWHM definition is realized. The maximum output power exceeds 4.6 W under continuous-wave operation at room temperature. The narrow circular beam emission from the BRL can greatly improve the pumping efficiency and optical fiber coupling efficiency without expensive beam shaping. It is believed that the BRLs have a promising application prospect.