Laser-Inscribed Diamond Waveguide Resonantly Coupled to Diamond Microsphere.

An all-diamond photonic circuit was implemented by integrating a diamond microsphere with a femtosecond-laser-written bulk diamond waveguide. The near surface waveguide was fabricated by exploiting the Type II fabrication method to achieve stress-induced waveguiding. Transverse electrically and transverse magnetically polarized light from a tunable laser operating in the near-infrared region was injected into the diamond waveguide, which when coupled to the diamond microsphere showed whispering-gallery modes with a spacing of 0.33 nm and high-quality factors of 105. By carefully engineering these high-quality factor resonances, and further exploiting the properties of existing nitrogen-vacancy centers in diamond microspheres and diamond waveguides in such configurations, it should be possible to realize filtering, sensing and nonlinear optical applications in integrated diamond photonics.

Silicon microsphere whispering gallery modes excited by femtosecond-laser-inscribed glass waveguides.

We report on the coupling of whispering gallery modes in a 500-µm-radius silicon microsphere to a femtosecond-laser-inscribed glass optical waveguide. The shallow glass waveguide with a large mode field diameter in the near-infrared is written at a depth of 25 µm below the glass surface, resulting in a high excitation impact parameter of 525 µm for the microsphere. The excited whispering gallery modes of the silicon microsphere have quality factors of approximately 105 in the 90° elastic scattering and 0° transmission. Integration of such spherical silicon microresonators on femtosecond-laser-inscribed glass waveguides is promising for photonic communication, computation, and sensing applications.

Spatial intensity profiling of elastic and inelastic scattering in isotropic and anisotropic liquids by immersion of a spherical silicon photocell.

The transverse spatial intensity distribution of elastic and inelastic light scattering in passive and active as well as weak and strong scattering liquid media has been studied by using Sphelar One p-n junction silicon spherical photocells. We immersed a Sphelar One in these scattering solutions and measured the photoconductive response in reverse biased photodiode (PD) configuration. The passive weak scattering medium was pure ethanol (EtOH), whereas the passive strong scattering medium was 5CB nematic liquid crystal (NLC). Solutions of 0.1 mM Rhodamine 640 perchlorate laser dye in EtOH and in 5CB NLC were used as active scattering media. The response of Sphelar One was strongly enhanced in 5CB NLC compared to EtOH, as well as in active solutions compared to passive solutions. The morphology of the Sphelar One is already advantageous over conventional one-sided planar PDs inside liquid solutions. This omnidirectional response of the Sphelar One can further be enhanced by optimizing the properties of the surrounding passive elastic and active inelastic scatterers.

Dynamical electrical tuning of a silicon microsphere: used for spectral mapping of the optical resonances.

In this work, electrical square pulses at various duty cycles are applied to a silicon microsphere resonator in order to continuously tune the refractive index of a silicon microsphere and to map the optical resonance in the time domain. A continuous-wave semiconductor diode laser operating in the L-band is used for the excitation of the silicon microsphere optical resonances. The 90° transverse magnetically polarized elastic scattering signal is used to monitor the silicon microsphere resonances. We show that at a constant input laser wavelength, up to five high-quality-factor optical resonances can be scanned by dynamical electrical tuning of the silicon microsphere cavity.

Geometrically enhanced morphology-dependent resonances of a dielectric sphere.

The effect that geometrical resonances of orbiting internally reflecting rays have on the morphology-dependent resonances of microspheres is investigated heuristically and numerically using generalized Lorenz-Mie theory. Angularly resolved off-axis Gaussian beam elastic scattering spectra are presented. The results obtained show that the elastic scattering intensity of morphology-dependent resonances is noticeably enhanced in the vicinity of the geometrical resonance scattering angles.

Liquid-crystal tunable filter based on sapphire microspheres.

We design an integrated optoelectronic device based on the whispering-gallery modes of a sapphire microsphere integrated with a liquid-crystal tuning medium to produce a narrowband, electrically tunable, channel-dropping filter. The sapphire microsphere is glued over a diffused waveguide in a glass substrate. At the base of the microsphere, a small volume of liquid crystal is infiltrated. We numerically evaluate the performance of the device and demonstrate a voltage tuning of the narrowband resonances.

Microdroplet identification and size measurement in sprays with lasing images.

Two-dimensional fluorescence and lasing images of a Rhodamine-6G doped water spray are observed with color photography. The orange-red lasing microdroplets are identified by their two reciprocal lasing spots. The microdroplet sizes are measured using the digitized images. The obtained microdroplet size distribution compares favorably with the normal Gaussian size distribution.

Photonic detection and characterization of DNA using sapphire microspheres.

A microcavity-based deoxyribonucleic acid (DNA) optical biosensor is demonstrated for the first time using synthetic sapphire for the optical cavity. Transmitted and elastic scattering intensity at 1510 nm are analyzed from a sapphire microsphere (radius 500 µm, refractive index 1.77) on an optical fiber half coupler. The 0.43 nm angular mode spacing of the resonances correlates well with the optical size of the sapphire sphere. Probe DNA consisting of a 36-mer fragment was covalently immobilized on a sapphire microsphere and hybridized with a 29-mer target DNA. Whispering gallery modes (WGMs) were monitored before the sapphire was functionalized with DNA and after it was functionalized with single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). The shift in WGMs from the surface modification with DNA was measured and correlated well with the estimated thickness of the add-on DNA layer. It is shown that ssDNA is more uniformly oriented on the sapphire surface than dsDNA. In addition, it is shown that functionalization of the sapphire spherical surface with DNA does not affect the quality factor (Q . ≈ 04) of the sapphire microspheres. The use of sapphire is especially interesting because this material is chemically resilient, biocompatible, and widely used for medical implants.