A light emitting device comprises a lightguide formed from a film with a core layer, a light emitting region, a light mixing region, at least one light source, and a light absorbing cladding region on at least one lateral edge of the core layer. In one embodiment, the cladding region is on the lateral edges of the core layer in the light mixing region. The light absorbing material in the cladding region may absorb light from the at least one light source propagating in the cladding region at an angle greater than 40 degrees to the optical axis. The difference in refractive index for the core material and cladding material may be between 0.001 to 0.01. The full angular width at half maximum intensity of light exiting the light emitting region may be less than 60 degrees in air in a first illumination plane.

A nonreciprocal Solar thermophotovoltaic (STPV) system includes an absorber configured to absorb broad-spectrum solar radiation and generate heat an intermediate emitter, and a single-junction photovoltaic cell configured to convert solar radiation to electrical energy. The intermediate emitter includes nonreciprocal radiative properties. The nonreciprocal radiative properties include absorbing light from the front side but only emitting light to the backside.

Embodiments of the invention include a method of initiating an optical fiber of a tip assembly to form a finished tip assembly. In some embodiments, at least a portion of a distal portion of the optical fiber is coated with an energy absorbing initiating material. In some embodiments, the initiating material is an enamel material including a mixture of brass (copper and zinc) flakes or aluminum flakes in a solution of organic solvents. After the initiating material dries, a diode laser is fired through the optical fiber. The laser energy is at least partially absorbed in the initiating material and ignites the organic solvents. This combustion melts the material of the optical fiber, and impregnates the optical fiber with the metal flakes of the initiating material. The resulting initiated optical fiber is thus permanently modified so that the energy applied through the fiber is partially absorbed and converted to heat.

Disclosed herein are methods, structures, apparatus and devices for the termination of unused waveguide ports in planar photonic integrated circuits with doped waveguides such that free-carrier absorption therein may advantageously absorb any undesired optical power resulting in a significant reduction of stray light and resulting reflections.