Single-photon sources are important elements in quantum optics and quantum information science. It is crucial that such sources be able to couple photons emitted from a single quantum emitter to a single propagating mode, preferably to the guided mode of a single-mode optical fiber, with high efficiency. Various photonic devices have been successfully demonstrated to efficiently couple photons from an emitter to a single mode of a cavity or a waveguide. However, efficient coupling of these devices to optical fibers is sometimes challenging. Here we show that up to 38% of photons from an emitter can be directly coupled to a single-mode optical fiber by utilizing the flat tip of a silica nanofiber. With the aid of a metallic mirror, the efficiency can be increased to 76%. The use of a silicon waveguide further increases the efficiency to 87%. This simple device can be applied to various quantum emitters.
We show that a hemispherically shaped tip on an air-clad optical fiber simultaneously works as a high-numerical-aperture lens and efficiently collects photons from an emitter placed near the beam waist into the fundamental guided mode. Numerical simulations show that the coupling efficiency reaches about 25%. We have constructed a confocal microscope with such a lensed fiber. The measurements are in good agreement with the numerical simulation. The monolithic structure with a high-photon-collection efficiency will provide a flexible substitute for a conventional lens system in various experiments such as single-atom trapping with a tightly focused optical trap.
We show that the output mode of a single-mode optical fiber can be directly focused to a subwavelength waist with a finite working distance by tapering the fiber to a diameter of the order of the wavelength and terminating it with a spherically/hemispherically shaped tip. We fabricate the micro-lensed fiber and construct a probe-scanning confocal reflection microscope. Measurements on a Chrome-plated test target clearly show tip size dependence of the resolution power of the microscope. Due to their monolithic structures, these micro-lensed fibers will be flexible substitutes for conventional compound lenses in various experimental conditions such as cryogenic temperature and/or ultra-high vacuum.
We have performed numerical simulations of photon coupling devices utilizing a nanofiber tip. It is shown that proposed devices can couple up to 38% of light from a point dipole source to the fundamental guided mode of a single-mode optical fiber. These devices can be applied for various kinds of single-photon emitter, including quantum dots, neutral atoms, and defect centers in diamond crystals.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.