Abstract: Apparatus for coupling light into a fiber, such as a double clad fiber (DCF) having a core having a refractive index n1, surrounded by an inner cladding having refractive index n2 which is surrounded by an outer cladding having a refractive index n3, where n1>n2>n3. An optical coupler medium, referred to as a Fiber Space Division Multiplexor or FSDM, is formed on an exposed portion of the fiber inner cladding at a position along the length of the fiber without interfering with the continuity of its core and provides at, at least one position, the imaging of light external of the fiber into the inner cladding interface and its waveguiding with the inner cladding of the fiber. The FSDM coupler comprises an optical material in optical contact or integrated with the inner cladding and having a refractive index substantially equal to n2. The coupler medium may also be employed with a fiber having no core and where the inner cladding would function as a multimode core.

Abstract: The effectiveness of reflected light to stabilize the operational characteristics of a semiconductor diode laser varies with the polarization orientation of the reflected light. Stabilization failure can occur if the polarization orientation of the reflected light is orthogonal to the polarization of the light emitted by the laser source. The use of multiple reflectors can reduce the probability of stabilization failure by arranging the reflectors to return to the laser source portions of light having polarization orientations that are statistically independent with respect to each other.