The present invention relates to a semiconductor laser apparatus for use as a light source for optical storage and optical communication applications.
As described in Appl. Phys. Lett., 57(10)966 (1990) by N. Bar-Chaim et al., the more recent prior art bent waveguide semiconductor laser apparatus forms a semiconductor laser cavity with the mirror surface of the same cleaved facet by suitably bending an optical waveguide having an optical gain conducive to constituting a semiconductor laser. Semiconductor laser apparatuses of this type appear to be effective when used by optical integrated devices because, unlike other traditional semiconductor laser apparatuses, the former are not limited in device size by cleavage requirements.
The above-mentioned more recent type of prior art semiconductor laser apparatus has its share of disadvantages. One disadvantage is that because the bent portion of the waveguide doubles as an optical gain region, it is difficult to meet simultaneously both the optimum design conditions for the optical gain region as part of the optical waveguide and the conditions for minimizing the bending loss of the optical waveguide. To obtain a high-output fundamental mode from the semiconductor laser apparatus requires that the optical waveguide be as wide as possible and that the difference in effective refractive index between the inside and outside of the optical waveguide be approximately between 1.times.10.sup.-3 and 5.times.10.sup.-3. Meanwhile, the effective refractive index difference of at least 1.times.10.sup.-2 is known to be needed to minimize the cavity loss of the bent portion. Another disadvantage of the prior art semiconductor laser apparatus is that changes in the direction of the optical waveguide in the optical gain region necessarily entail varied etching shapes and crystal growth shapes of the semiconductor crystal employed.