A light source module of an optical apparatus is disclosed. The light source module includes a laser pump unit, a lens unit, and a fiber unit. The laser pump unit generates a laser source. The lens unit converts the laser source into a condensed beam. The fiber unit receives the condensed beam and emits an optical signal. The light source module can achieve effects of low cost, large bandwidth, high resolution, and high stability with well-designed pump power of the laser pump unit, and length, doping material, and core size of the fiber unit.