Pre-assembled whispering gallery mode resonance sensors, for use as dip sensors or vapor sensors, for example, and methods for making such sensors

#§2.1 Field of the Invention

#The present invention concerns whispering gallery mode (“WGM”) sensors that can detect the presence of, identify the composition of, and/or measure an amount or concentration of substances (referred to generally as “target entities,” “target analytes,” or simply “targets”), such as chemical or biological entities. The present invention also concerns methods and apparatus to make, and/or use such WGM sensors.

#§2.2 Background Information

#FIG. 1 illustrates that when light travels within a transparent medium of a circular cross section on a track near the surface of the medium by total internal reflection, the light superimposes onto itself after one cycle.

#FIGS. 2A-2D illustrate how a WGM sensor utilizes a shift of resonance wavelength that occurs when a target binds to a receptor on the surface of the resonator.

#FIG. 3 illustrates how past studies of WGM biosensors and chemosensors used a fluidic device that holds a fluid permeating a resonator.

#FIG. 4 is a perspective, semi-transparent, view of an example WGM sensor head 400 (or simply referred to as a “WGM sensor” or a “sensor”) consistent with the present invention. As is the case with some conventional WGM sensors, the example sensor includes a resonator 410, a feed fiber 420 and a pickup fiber 425. (Note that most conventional WGM sensors use a single through taper, which both feeds light into the resonator, and picks up light from the resonator.) However, the example WGM sensor of FIG. 4 further includes a stem 430, a spacer 440, and an outer capillary 450 (or outer tube).

#Each of the two fibers 420/425 is honed to a cone 421/426. The tips of the cones 421/426 touch the resonator 410. The feed fiber 420 feeds light (e.g., sourced from a laser, not shown) into the resonator 410, and the pick-up fiber 425 picks up the light in the resonator 410 (e.g., for measurement by a detector, not shown).

#The resonator 410 is attached to a stem 430 and has a circular cross section. In the example embodiment illustrated, the resonator 410 is a microsphere. The axis of the resonator 410 normal to its circular cross section defines an angle of about 90° with the stem. Other angles (for example, a range of 70-110 degrees, and more preferably a range of 80-100 degrees) are possible, provided that the stem 430 does not interfere with the optical resonance at the equator (or circular cross section) of the resonator 410.