KR20070018083A - Dielectric Microcavity Fluorescent Sensor Excited with Broadband Light Source - Google Patents

Abstract

The microresonator sensor device of the present invention has a microcavity resonator defining an equatorial whispering gallery mode (EWGM) whose frequencies are separated by a free spectral region (FSR). The EWGM lies in a plane perpendicular to the microcavity resonator axis. The light source is optically coupled to inject light into the microcavity resonator. The light source produces output light having an output spectrum whose bandwidth is approximately equal to or greater than the FSR of the EWGM. One or more fluorescent materials are excited using excitation light coupled to the microcavity resonator. The fluorescence signal resulting from the fluorescence of one or more fluorescent materials is then detected.

Microcavity resonator, microresonator, fluorescent sensor, whispering gallery mode (WGM), equatorial whispering gallery mode (EWGM)

Description

DIELECTRIC MICROCAVITY FLUOROSENSORS EXCITED WITH A BROADBAND LIGHT SOURCE}

FIELD OF THE INVENTION The present invention relates generally to optical devices and, more particularly, to optical sensors using microresonators.

Dielectric microspheres have attracted increasing attention as fluorescent sensors in recent sensor applications. In these sensors, the sensor surface is immobilized with a layer of molecules such as an antibody for subsequent capture of the analyte, such as an antigen. In a direct assay configuration, the antigen is associated with a fluorescent dye molecule. When the antigen binds to the antibody on the sensor surface, the fluorescent molecule is excited by evanescent light that remains close enough to the microspheres and circulates within the microspheres. In the sandwich configuration, the antigen is first bound to the antibody on the sensor surface, and then a second antibody layer with fluorescent dye attached is added to bind the captured antigen. Fluorescent molecules bound to the second antibody layer are excited by an evanescent field resulting from light propagating in the whispering gallery mode (WGM) of the microspheres. Fluorescence generated from the excited dye is collected and used as an indicator of antigen binding events.

The microsphere's WGM is associated with a high Q-factor, so that the intensity of the light when coupled to the WGM is enhanced compared to the input light. The degree of augmentation is proportional to the Q-factor. In general, a narrow bandwidth tunable semiconductor diode laser having a sub-megahertz spectral linewidth is used as the light source to excite the WGM in the microsphere cavity. The bandwidth of the laser light is comparable to the bandwidth of a single WGM resonance. Thus, when the laser is tuned to a specific WGM resonance, most of the combined light falls within the resonance bandwidth, thus there is an efficient coupling to the WGM resonance. However, the high cost of such lasers has proven to be a significant obstacle to the widespread introduction of microsphere-based sensors in many applications.

Thus, one particular embodiment of the present invention is a microcavity defining an equatorial whispering gallery mode (EWGM) in which the frequencies are separated by a free spectral range (FSR). A micro resonator sensor device comprising a resonator. The EWGM lies in a plane perpendicular to the microcavity resonator axis. The light source is optically coupled to inject light into the microcavity resonator. The light source produces output light having an output spectrum whose bandwidth is approximately equal to or wider than the FSR of the EWGM.

Another embodiment of the invention is directed to a method of making fluorescence measurements comprising coupling excitation light to a first microcavity resonator. The first microcavity resonator defines Equatorial Whispering Gallery Modes (EWGMs), the excitation light having a bandwidth wide enough to be able to couple to at least two adjacent EWGMs. One or more fluorescent materials are excited using the excitation light coupled to the first microcavity resonator. The fluorescence signal resulting from the fluorescence of the one or more fluorescent materials is then detected.

The above disclosure of the present invention is not intended to describe each illustrated embodiment or every embodiment of the present invention. The following figures and detailed description more particularly exemplify these embodiments.

The invention may be more fully understood by considering the following detailed description of various embodiments of the invention in connection with the accompanying drawings.

1A-1C schematically illustrate different embodiments of microcavity sensors in accordance with the principles of the present invention.

2 schematically illustrates a whispering gallery mode in a microcavity resonator.

3A-3C schematically illustrate cylindrical, spherical and bulge-like microcavities, respectively.

4A-4C schematically depict portions of the microcavity resonant spectrum illustrated in FIGS. 3A-3C, respectively.

5A shows the bandwidth of an exemplary light source.

5B shows the bandwidth of a light source emitting light in a resonant mode.

Figure 6 shows the resonant spectra of microcavities measured using narrowband light from a tunable semiconductor laser.

7 shows the time dependence of the fluorescence signal obtained from the microcavity when excited with broadband light.

While the invention is susceptible to various modifications and alternative forms, details thereof are shown by way of example in the drawings and will be described in detail. However, it should be understood that the invention is not limited to the specific embodiments described. However, the invention will encompass all modifications, equivalents, and substitutions falling within the spirit and scope of the invention as defined by the appended claims.

The present invention is particularly applicable to an optical sensor using a microcavity resonator. Such resonators may also be called microresonators.

In contrast to narrow bandwidth tunable diode lasers, semiconductor light sources with wider line widths are relatively inexpensive. Until now, wideband light sources have been considered unsuitable for applications with high Q factor microspheres, since only a small fraction of the output light from such light sources spectrally overlaps with the single whispering gallery mode (WGM) resonance of the microspheres. This is because the augmentation given by the microspheres can be experienced.

Broadband light sources, however, are suitable for use with microcavities when the cavitation mode density of the microcavities is high and light is coupled to multiple WGMs. In such a situation, a significant portion of the output from the broadband light source can be coupled to the microcavity, so the combination of the broadband light source and the microcavity leads to a high sensitivity fluorescent sensor with low associated component costs.

An example of a microcavity-waveguide system 100 using a microresonator is schematically illustrated in FIG. 1A. The light source 102 directs light along the waveguide 104 to the detector unit 106. Microresonator 110 is optically coupled to waveguide 104. Light 108 from light source 102 exits waveguide 104 and propagates toward detector unit 106. The microresonator 110 loses and couples a portion of the light 108 to the outside of the waveguide 104, and the externally coupled light 112 is one of the resonant frequencies of the microresonator 110 within the microresonator 110. Propagates at a frequency.

The light source 102 can be any suitable type of light source. For increased efficiency and sensitivity, it is advantageous for the light source to produce light that is efficiently coupled to the waveguide 104, for example the light source may be a laser, such as a laser diode, or may be a light emitting diode. Light source 102 generates light 108 of a desired wavelength, or range of wavelengths. For example, when a microresonator is used in the sensor, the light source 102 generates light of a wavelength that interacts with the species being sensed. The sensed species are typically placed in close proximity to the surface of the microresonator 110 such that the light propagating in the WGM interacts with the sensed species. Light source 102 may also include a lamp together with a suitable optical device for coupling light from the lamp into waveguide 104.

For example, when the system 100 is used as a fluorescence sensor, light propagating in the microresonator 110 may be directed to an analyte on the microresonator surface or to a marker indicating the presence of the analyte. It is absorbed by fluorescent molecules, such as fluorescent dyes, to which they are attached. In a more specific example, the antibodies may be attached to the surface of the microresonator specific to the desired antigen analyte. The analyte antigen molecules combined with the fluorescent dye are introduced into the sensor system 100. The antigen molecules bind to antibody molecules on the microresonator 110, thus keeping the fluorescent dye molecules close enough to the microresonator 110 so that light circulating within the microresonator 110 is lost to the fluorescent molecules. . The absorbed light excites the fluorescent molecules, which then fluoresce at a wavelength different from the excitation wavelength. Detection of fluorescent light confirms the presence of the analyte antigen.

In another example, the analyte antigen molecules are not bound to the fluorescent dye, but are allowed to bind to the antibody attached to the microresonator surface. Then more antibodies bound to the fluorescent molecules are introduced into the sensor to bind the antigen. Again, fluorescent molecules are excited by the lossy interaction with light propagating within microresonator 110, and subsequent detection of fluorescence can be used to determine the presence and abundance of the analyte antigen.

Light source 102 may direct light to a number of different waveguides, of which waveguide 104 is one such example. Waveguide 104 may be any suitable type of waveguide and may be, for example, a planar waveguide or channel waveguide formed in or on a substrate, such as a waveguide formed in a silica substrate. Waveguide 104 may also be an optical fiber.

The detector unit 106 comprises a photo detector for detecting light, for example a photodiode or phototransistor. The detector unit 106 may also include a wavelength selection device for selecting the wavelength of light reaching the photo detector. The wavelength selection device may be, for example, a filter or a spectrometer. The wavelength selection device may be tunable to allow the user to actively change the wavelength of light incident on the photo detector.

Microresonator 110 is in physical contact with waveguide 104 or very close to waveguide 104 such that a portion of the light 108 propagating along waveguide 104 is lost and coupled into microresonator 110. Can be arranged. Waveguide 104 typically has little or no cladding at the point where microresonator 110 couples to waveguide 104, so microresonator 110 couples directly to the core of waveguide 104. do.

Another type of microresonator device 150 is schematically illustrated in FIG. 1B. In this device 150, light 158 from the microresonator 110 is coupled to the second waveguide 154 and propagates to the detector 106.

Another type of microresonator device 170 is schematically illustrated in FIG. 1C. In this device 170, a second detector 172 is disposed close to the microresonator 110 to detect light from the microresonator 110. The light detected by the second detector 172 is not transmitted to the second detector 172 through the waveguide, but propagates through the free space. Light from the microresonator 110 detected by the second detector 172 may be scattered outside of the microresonator 110, for example, or by light circulating in the microresonator 110. And fluorescent light resulting from the excitation of fluorescent species, attached to the surface of the microresonator. The second detector 172 may detect all wavelengths of light from the microresonator 110 or use, for example, a wavelength selection element 174 located between the second detector 172 and the microresonator 110. It is also possible to detect light in a specific wavelength range. The wavelength selection element 174 may be, for example, a filter that rejects light of an excitation wavelength resonating in the microresonator 110 and transmits light of a fluorescent wavelength. The second detector 172 may also be used in a configuration such as that shown in FIG. 1B.

Light propagates in so-called "whispering gallery modes" in a microresonator, an example of which is schematically illustrated in FIG. In whispering gallery mode (WGM) 202, light propagates around the microresonator 210 until it returns to the origin via multiple total internal reflections from the origin. In the illustrated embodiment, the WGM 202 includes eight total internal reflections in a single round trip. It will be appreciated that light may propagate in other WGMs corresponding to different numbers of total internal reflections within the microresonator 210.

In addition, the WGM 202 demonstrates a high Q-factor if only light of such wavelength is light that constructively interferes after one revolution. In other words, the optical path length around the WGM 202 is equal to integer wavelengths. This resonance condition for light in the planar WGM 202 illustrated in FIG. 2 can be mathematically represented as follows.

[Equation 1]

lλ _l = L

Where λ _l is the wavelength of the l-th mode in vacuum, L is the optical length of one revolution of the WGM, and l is an integer called the mode number. Light from the waveguide 104 satisfying the resonance condition [Equation 1] is efficiently coupled to the microresonator. For the resonant mode of microcavities, see, for example, in volume 10, pp. 343-352, of the American Journal of Optics, 1993. egg. "Theory of morphology-dependent resonances: shape resonances and width formulas", described by BR Johnson, and Vol. 20, 1515-1517, Optical Paper, 1995. On the page, Jay. Seed. It is further described in "Mapping whispering-gallery modes in microspheres with a near-field probe" described by JC Knight et al.

The field strength of the WGM reaches its maximum at the inner surface of the microresonator 210. The field strength of the WGM is exponentially attenuated outside of the microresonator 210 and the characteristic attenuation length d is given by approximately d ≒ λ / n, where λ is the wavelength of light in vacuum and n is the microresonator 210. The refractive index of the external medium. The electric field strength E is schematically illustrated in FIG. 2 with respect to the WGM 202 along the section line AA '.

Microresonators 210 typically have diameters ranging from 20 μm to several millimeters, although the range of 50 μm-500 μm is more common. In addition, waveguides are often tapered to increase the intensity of photoelectric field strength outside the waveguide, thereby increasing the amount of light that couples to the microresonator. In the case of an optical fiber waveguide, the fibers may be heated and tapered or etched to a total thickness of about 1-5 μm. Likewise, in a planar or channel waveguide, the waveguide thickness can be reduced in the region where light is coupled to the microresonator. In addition to the size of the waveguide, the thickness of the cladding around the waveguide can be reduced. Various methods of coupling microresonators to waveguides or fibers are discussed in more detail in co-owned co-pending US patent application Ser. No. 10 / 685,049, incorporated herein by reference.

Different types of microcavity resonators will now be described with reference to FIGS. 3A-4C. The WGMs 306, 316, and 326 shown in Figures 3A-3C correspond to WGMs having only a single number of total internal reflections.

3A schematically illustrates a cylinder type microresonator 300, having a long axis 302 lying parallel to the circular wall 304 of the cylindrical microresonator 300. Such a microresonator may be formed using, for example, an optical fiber, in which light is tangentially coupled to the side of the fiber in a direction perpendicular to the fiber axis. The WGM 306 lies in a plane perpendicular to the axis 302 and is shown in dashed lines. Cylindrical microresonator 300 does not support the WGM mode, which lies in a plane that is not perpendicular to the axis because such light escapes from the resonant cavity without following a closed path. Since the WGM 306 lies in a plane perpendicular to the axis 302, the WGM may be referred to as the Equatorial WGM (EWGM).

Thus, the resonance spectrum of the EWGM 306 is as shown in FIG. 4, showing the graphed resonance as a function of the frequency ν. The l-th resonant mode is separated from the (l + 1) th resonant mode by a separation such as Δυ, also called the free spectral region FSR, where Δυ corresponds to an increase of 1 in the number of wavelengths around the EWGM 306. FSR can be calculated by frequency according to the following equation:

[Equation 2]

FSR = Δυ = c / L ≒ c / (πnD)

Where c is the speed of light in the vacuum, n is the refractive index of the microcavity, D is the cylinder diameter, and nπD approximates the optical length of one revolution of the EWGM. The lth and (l + 1) th modes are called adjacent EWGM modes.

FSR can also be expressed by wavelength:

[Equation 3]

FSR (in wavelength) = Δυλ ² / c = λ ² / (πnD)

Is the wavelength of light in a vacuum. Both definitions of FSR are used interchangeably in the present invention.

The other EWGM has a different number of total internal reflections and therefore different optical path lengths than that of the mode shown. The resonant frequencies associated with these other EWGMs are different from the resonant frequencies shown in FIG. 4A.

3B schematically illustrates a spherical microresonator 310 located on an axis 312. Such microresonators may be formed using, for example, glass spheres having spherical walls 314. EWGM 316 lies in a plane perpendicular to axis 312 and is shown in dashed lines. The resonance spectrum of the EWGM 306 is illustrated in the graph shown in FIG. 4B. Similar to the EWGM 306 of the cylindrical resonator, the frequency spacing between adjacent resonances is given by Δυ (FSR), where Δυ corresponds to an increase of 1 in the number of whole integer wavelengths around the EWGM 316. FSR is given by Equation 2 above, where D is the diameter of the spherical microresonator 310.

However, unlike planar microresonators, spherical microresonators 310 support WGMs that are not perpendicular to axis 312. One such WGM 318 is shown (in dashed lines) lying at an angle θ with respect to the WGM 316. WGM 318 is called non-equatorial mode, or azimuth mode. However, since the microresonator 310 is spherical, the path length of the WGM 318 is the same as the path length of the EWGM 316, so the resonant frequencies for the WGM 318 are the same as for the EWGM 316. Since the frequency of the non-equal mode is the same as the EWGM, the non-equal mode is said to degenerate in frequency.

Other resonant spectra corresponding to the EWGM with different numbers of total internal reflections have a different resonant frequency than the resonant frequency shown in FIG. 4B.

3C schematically illustrates a microresonator 320 that is neither cylindrical nor spherical. In the illustrated embodiment, the microresonator 320 has an elliptical wall 324. Microresonator 320 is located on shaft 322. The EWGM 326, which lies in a plane perpendicular to the axis 322, is shown in dashed lines. Some of the resonances of the equatorial EWGM 326 are schematically shown as resonances 327 in the graph shown in FIG. 4C. The frequency spacing between adjacent resonances 327 of the EWGM 326 is given by Δν (FSR), where Δυ corresponds to an increase of 1 in the number of whole integer wavelengths around the EWGM 326. FSR is given by the above Equations 2 and 3, where nπD approximates the optical path length of one revolution of the EWGM.

However, if the optical path of the mode is tilted through the angle θ from zero to form a non-equatorial path, then the resonance associated with this non-equatorial path is not the same as that for the equatorial mode. This is because the path length around the elliptical microresonator changes as θ increases from zero. In other words, the path length for the equatorial mode is different from the path length for the non-equitous mode. Thus, different non-equatorial WGMs have different resonant frequencies that vary with the value of θ. Thus, the resonant spectrum for the microresonator 320 may cause multiple resonances 329 for the non-equatorial mode to “fit-in” the regions between the resonance 327 in the equatorial mode. Include. Note that only a few non-equatorial resonances are included in FIG. 4C, and the representation of the non-equatorial resonance 329 in FIG. 4C is given for qualitative purposes only. For the purpose of distinguishing between an equatorial resonance and a non-equatorial resonance, FIG. 4C shows that the size of the non-equiral resonance 329 is smaller than the size of the equatorial resonance 327. However, there is no intention to indicate that the non-equatorial resonance 329 has a different Q-factor than the equatorial resonance 327. In such a case, when a broadband light source is used, the total light intensity in the microcavity is augmented by a factor proportional to the number of modes that fit into one FSR.

One type of microcavity resonator with a wide range of cavity resonant frequencies is a bulge type microcavity, X. X. Fan and Egg. It is described in more detail in dielectric microcavity sensors, agent case number 59632US002, filed on the same day as the present application by R. Wilson, and incorporated herein by reference.

The light coupled into the microcavity may have a relatively broad spectrum, for example, approximately equal to or greater than Δν, which is the FSR of the microcavity EWGM. The bandwidth of light is typically measured as its full width, half maximum (FWHM) bandwidth (see Figure 5A). When light is generated at the laser, the light spectrum includes a number of discrete modes 502, corresponding to the Fabry-Perot resonance of the laser, which lies within the amplitude envelope 504. See also a schematic illustration of FIG. 5B. In such a case, the bandwidth of the light is the FWHM bandwidth of the envelope 504.

In conventional cylindrical microresonators, the coupling of light from the waveguide to the microresonator is sensitive to the alignment between the waveguide and the microresonator: if the light is not injected into the microresonator's equatorial mode, the light enters the low Q mode and will quickly be lost. Can be. However, the coupling of light is less sensitive to the alignment of the bulge cavities with respect to the waveguide, since the bulge cavities provide light confinement in three dimensions rather than just two dimensions as in cylindrical microcavities. In addition, waveguides that couple light to the cylindrical microcavities are typically relatively narrow, although they may have a large lateral range along the cylindrical axis when the cylindrical microcavities are formed of, for example, optical fibers. Relatively wider waveguides support a greater number of transverse modes, thus increasing the likelihood that light from the waveguides enters and disappears into cylindrical microcavity non-equatorial WGM. However, wider waveguides can be used with bulge microcavities because the three-dimensional confinement properties of the bulge microcavity allow efficient excitation of non-equatorial modes with high Q. The use of wider waveguides can lead to improved light coupling efficiency for light between light source and waveguide and between waveguide and microcavity.

Thus, the use of a non-cylindrical microresonator leads to the presence of a cavity resonance with resonant frequencies of more different values than cylindrical microcavities. Also, non-spherical microcavities do not show the same frequency degeneration as spherical microcavities. As a result, non-spherical microcavities (with non-equatorial modes with non-degenerate frequencies) result in an increase in the number of different frequencies at which resonance can occur. Such a microcavity resonator can demonstrate the presence of a larger number of resonances per unit frequency compared to the cylindrical or spherical microresonators of FIGS. 3A and 3B. However, it is difficult to obtain a completely spherical microcavity, and even small aspherical formation in the microcavity leads to the destruction of the degeneracy. Thus, light from the broadband light source can be efficiently coupled to multiple cavity resonance modes. Examples of broadband light sources include semiconductor lasers and light emitting diodes, such as semiconductor lasers with Fabry-Perot cavities. Such broadband light sources are considerably less expensive than tunable semiconductor lasers that produce light with an output bandwidth of less than 1 MHz. Thus, in one exemplary embodiment, light may be supplied by a light source having a bandwidth approximately equal to or greater than one FSR of the EWGM of the microresonator. In another exemplary embodiment, the bandwidth of the light may be at least five times greater than the FSR, and in another exemplary embodiment, at least ten times greater than the FSR.

Yes

Experiments were performed in comparison to irradiation with a broadband broadband light source with a narrower frequency width and with a tunable semiconductor diode laser. The experimental setup was similar to that illustrated in FIG. 1C, and the light source guided light in the range of 630-635 nm through the tapered fibers as a coupling waveguide. The fiber core was tapered to a diameter of about 1.5 μm-2.5 μm. The first detector was positioned to detect light transmitted along the waveguide past the microcavity. A second detector was arranged to detect free space emission of light from the microcavity.

A glass microcavity having a diameter of about 150 μm was formed by melting the tip of the SFM28 optical fiber with a CO ₂ laser. The free microcavities were close to spherical and attached biotinated bovine serum albumin (BSA). A sample of streptavidin was attached to Alexa Fluor 647 as a phosphor. Streptavidin samples with a concentration of 800 pM (50 ng / ml) were introduced into the microcavities. Streptavidin binds to biotin on the microcavity surface, binding the phosphor to the microcavity.

Microcavities were first irradiated with combined light from a tunable semiconductor laser that was tunable over at least the range of 630 nm-633 nm. 6 shows the spectra obtained from the two detectors when the laser was scanned over a range of about 25 pm. The upper curve labeled 602 corresponds to the signal detected by the first detector. The dip in the detection signal corresponds to the resonance of the microcavities. The microcavity free spectral region (FSR) was calculated using Equation 3.

[Equation 3]

FSR (in wavelength) = Δυλ ² / c = λ ² / (πnD)

Where c is the speed of light in vacuum, λ is the wavelength of light in vacuum, n is the refractive index of the microcavities, and D is approximately close to the diameter of the spherical microcavities. For the microcavities used in the experiments, the FSR was approximately 580 pm.

The lower curve labeled 604 corresponds to the free space fluorescence signal detected by the second detector disposed close to the microcavity. The fluorescence peaks in curve 604 correspond to the excitation of the phosphor at the resonant frequency of the microcavity.

In the next experiment, a microcavity with a diameter of about 250 μm, with an accompanying FSR of about 350 pm, was irradiated using light from a laser diode with an output bandwidth of 635 nm and an output bandwidth of 0.5 nm (500 pm). It became. In this particular example, the bandwidth of the light output from the laser is greater than a single FSR. The optical power coupled to the fiber taper was approximately 250 μW.

 A streptavidin sample with a concentration of 8 pM (500 pg / ml) was introduced to the surface of the microcavity. The response of the second detector that detected the free space fluorescence signal is provided in the graph of FIG. 6 as a function of time. The excitation light was initially blocked at the input to the tapered fiber, so no light was coupled to the microcavity (point A). Thus, the signal level at point A is approximately 0.03V, corresponding to the level of background noise in the signal from the second detector.

When the excitation light was unblocked at point B, a strong fluorescence signal was observed. This corresponds to a phosphor that emits light as a result of being excited by light resonating in the microcavity. The signal at point B is approximately 3V, so the signal-to-noise ratio was about 100. The light from the laser diode was cut off and the fluorescence signal was detected using a fixed phase amplifier.

After an excitation time of approximately 180-200 seconds, the fluorescence signal dropped to a level of about 0.08 V. This reduction in signal intensity over time was due to the bleaching of the dye molecules.

These experimental results demonstrate the detection of streptavidin (with Alexa Fluor 647 attached) with concentrations as low as 8 pM (500 pg / ml), where the light source had a larger bandwidth than the microcavity FSR. The detection limit is estimated to be approximately 80 fM (5 pg / ml), everything else is the same. It is expected that even lower detection limits can be achieved if the phosphor is integrated with a fluid system for more efficient sample delivery.

The experiment described above shows that instead of a tunable narrowband light source, a wideband light source can be used efficiently in fluorescence detection measurements. The use of broadband light sources, for example light sources whose output light has a bandwidth greater than the free spectral region of the WGM, can lead to significant savings in component costs of the microcavity fluorescent sensor system.

Accordingly, the present invention should not be considered limited to the specific embodiments described above, but rather should be understood to cover all aspects of the invention as duly set forth in the appended claims. Various modifications, equivalent processors, as well as numerous structures to which the present invention may be applied will be readily apparent to those skilled in the art upon reviewing this specification. The claims are intended to cover such modifications and devices.

Claims (29)

Micro Resonator Sensor Device A microcavity resonator whose frequencies are separated by a free spectral region (FSR) and which define the equatorial whispering gallery modes (EWGM) lying in a plane perpendicular to the microcavity resonator axis, And a light source optically coupled to inject light into the microcavity resonator and generating output light having an output spectrum whose bandwidth is approximately equal to or greater than the FSR of the EWGMs. The microresonator sensor device of claim 1, wherein the microcavity comprises a bulge type microcavity resonator. 3. The microresonator sensor device of claim 2, wherein the bulge-type microcavity resonator extends along an axis and further comprises a waveguide coupling the output light from the light source to the microcavity resonator. The microresonator sensor device of claim 1, further comprising a first optical waveguide disposed to couple light from the light source to the microcavity resonator. The microresonator sensor device of claim 4, wherein the first optical waveguide comprises a tapered optical fiber. 5. The microresonator sensor device of claim 4, wherein the first optical waveguide comprises a planar waveguide on the substrate. 5. The microresonator sensor device of claim 4, further comprising at least a first photo detector arranged to detect light associated with the first microcavity resonator. 8. The microresonator sensor device of claim 7, wherein the first photodetector is optically coupled to receive light propagating along the first optical waveguide from the microcavity resonator. 8. The microresonator sensor device of claim 7, wherein the first photo detector is disposed in proximity to the microcavity resonator to detect light propagating through the free space from the microcavity resonator. 8. The microcavity of claim 7, further comprising a second optical waveguide optically coupled to the microcavity resonator, wherein the first photodetector is optically coupled to receive light propagating along the second optical waveguide from the microcavity resonator. Resonator sensor device. 8. The microresonator sensor device of claim 7, further comprising a wavelength selection element arranged to select a wavelength of light propagating to the first photodetector. The microresonator sensor device of claim 1, wherein the light source comprises a semiconductor laser. The microresonator sensor device of claim 1, wherein the light source comprises a light emitting diode. 2. The microresonator sensor device of claim 1, wherein the bandwidth is at least five times the FSR. 2. The microresonator sensor device of claim 1, wherein the bandwidth is at least 10 times the FSR. Coupling an excitation light having a bandwidth wide enough to be capable of coupling to at least two adjacent EWGMs, to a first microcavity resonator defining equatorial whispering gallery modes (EWGMs), Exciting one or more fluorescent materials using excitation light coupled to the first microcavity resonator, Detecting a fluorescence signal resulting from the fluorescence of one or more fluorescent materials. 17. The method of claim 16, wherein combining the excitation light comprises generating the excitation light using a light source and passing the excitation light from the light source through the optical waveguide to the microcavity resonator. 18. The method of claim 17, wherein generating excitation light comprises generating excitation light at a laser. 18. The method of claim 17, wherein generating excitation light comprises generating excitation light at a light emitting diode. The method of claim 17, wherein the optical waveguide comprises tapered fibers. The method of claim 17, wherein the optical waveguide comprises a planar waveguide on the substrate. 17. The method of claim 16, wherein detecting the fluorescence signal comprises detecting light propagating in free space from the microcavity resonator. 17. The method of claim 16, further comprising optically filtering the fluorescent signal prior to detecting the fluorescent signal. The method of claim 16, wherein the light source comprises a semiconductor laser. The method of claim 16, further comprising attaching the analyte to the microresonator cavity, wherein the fluorescent material is associated with the analyte. 27. The method of claim 25, further comprising attaching a fluorescent material to the analyte before attaching the analyte to the microresonator cavity. 27. The method of claim 25, further comprising attaching a fluorescent material to the analyte after attaching the analyte to the microresonator cavity. The method of claim 16, wherein the excitation light has a bandwidth wide enough to be able to couple to at least five adjacent EWGMs. The method of claim 16, wherein the excitation light has a bandwidth wide enough to be able to couple to at least ten adjacent EWGMs.

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