News Column

"Broad-Spectrum Illuminator for Microscopy Applications, Using the Emissions of Luminescent Materials" in Patent Application Approval Process

September 10, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- A patent application by the inventor Lee, Ho-Shang (El Sobrante, CA), filed on November 5, 2013, was made available online on August 28, 2014, according to news reporting originating from Washington, D.C., by VerticalNews correspondents.

This patent application is assigned to DiCon Fiberoptics, Inc.

The following quote was obtained by the news editors from the background information supplied by the inventors: "The present invention relates generally to illumination for microscopy applications, including both fluorescence microscopy and general microscopy applications, and specifically to an illumination apparatus that uses phosphor emissions to provide broad-spectrum white light. By using multiple phosphor types, the illumination apparatus provides a broad-spectrum light output that is highly suitable for exciting the large variety of fluorescent dyes that are used in fluorescence microscopy applications, from a single illuminator. In addition, the illuminating apparatus can provide high-quality white light for brightfield viewing in general microscopy applications, including visible light image capture and photography.

"Fluorescence microscopy is popularly used in numerous bio/medical applications since it enables users to label and observe specific structures or molecules. Briefly, fluorescence is a chemical process in which light of a specific wavelength or wavelength range is shined upon a fluorescent molecule, causing electrons from said fluorescent molecule to be excited to a high energy state, in a process known as excitation. These electrons remain briefly in this high energy state, for roughly a nanosecond, before dropping back to a low energy state and emitting light of a longer wavelength. This process is referred to as fluorescent emission, or alternatively as fluorescence.

"In a typical fluorescence microscopy application, one or more types of fluorescent materials or molecules (also referred to as fluorescent dyes) are used, along with an illuminator apparatus that provides the exciting wavelength, or wavelengths. Different fluorescent molecules or dyes can be selected to have visually different emission spectra. Since the different fluorescent molecules or dyes that are typically used in fluorescence microscopy applications typically have different excitation wavelengths, they can be selectively excited so long as the bandwidth of the excitation light for one fluorescent molecule or dye does not overlap the excitation wavelengths of other fluorescent molecules or dyes that are being used in the same experiment. This is typically achieved by using specific wavelength-range bandpass filters to create narrow bandwidth excitation light. Broadband excitation light may also be used to simultaneously excite multiple fluorescent dyes. Furthermore, fluorescence is a probabilistic event with low signal levels so an intense light is typically used to increase the chances of the process occurring. Most fluorescence microscopy applications also benefit from having a uniformly intense illuminated field of view or area, ideally such that the size and shape of the illuminated area can be modified. Simultaneously achieving all these criteria has been difficult, but is necessary for current and future applications that require increasing levels of illumination control and consistency.

"Traditional prior art fluorescence microscopy illuminators have relied on metal halide arc lamp bulbs such as Xenon or Mercury bulbs, as light sources. The broad wavelength spectrum produced by these lamps, when combined with specific color or bandpass filters, allows for the selection of different illumination or excitation wavelengths. Alternatively, multiple fluorescent dyes, with different excitation and emission wavelengths, may be simultaneously excited. In this type of implementation using metal halide arc lamp bulbs, the speed with which different wavelengths can be selected is limited by the mechanical motion of moving various filters into place. In addition to the sluggishness and unreliability of filter wheels, metal halide arc lamps are also hampered by the limited lifetime of the bulb, typically .about.2000 hours. The intensity of the light output declines with bulb use and once exhausted, the user has to undergo a complicated and expensive process of replacing the bulb and subsequently realigning the optics without any guarantee that the illuminator will perform as before. These disadvantages make acquiring consistent results difficult and inconvenient for users who must deal with the variable output of the bulbs, and who must either be trained in optical alignment or call upon professionals when a bulb needs to be replaced. In addition, metal halide arc lamps produce substantial heat, including radiated emissions in the infrared region that can cause heating of the illuminated specimens. This can lead to specimen damage, especially in the case of biological specimens. Similarly, radiated emissions in the UV region may also harm specimens. (In both cases, the use of appropriately designed excitation filters can prevent specimen exposure to damaging wavelengths.)

"In recent years, several prior art multiple wavelength illuminators have been developed using different colored LEDs as light sources, that overcome numerous limitations of metal halide arc lamps. Not only do they last longer, with the lifetime of an LED chip being typically rated at well over 10,000 hours, but in addition the power output varies negligibly over that period. Furthermore, the bandwidth of the spectral output of an LED chip is typically narrow (

"Prior art LED illuminators for fluorescence microscopy have thus far used up to 5 separate LED modules, each containing one, up to a few chips, for each wavelength. Since the LED chips in these modules have their own individual packaging, the modules are large so that light beams emitted from the modules will need to be combined using optical elements. Although such prior art LED illuminators allow the user the flexibility to swap out modules for new modules with different wavelengths, the additional elements such as lenses, mirrors and heat sinks required for each separate color add complexity, bulk and cost. Furthermore, the long optical paths required to combine the beams from multiple LED chips or modules that are spatially separated, make it difficult to collect and shape already highly divergent light coming from the LED chips. Even when multiple LEDs are packaged or mounted close to each other, the light output of LED chips that are located even a short distance away from the optical axis will be poorly coupled to the objective lens of the microscope.

"Another limitation of prior art LED illuminators for fluorescent microscopy is that there is a 'dead zone' in the visible light spectrum, where LED chips are either not readily available, or are of very limited optical output. This dead zone is roughly in the portion of the visible light spectrum that lies between green and amber (or orange), in the approximate wavelength range of 540-595 nm. Unfortunately, several popular fluorescent dyes require excitation light that is in this dead zone.

"These practical issues have limited the application of such illuminators in fluorescence microscopy, which in general requires light that is both intense and spatially uniform, across the full range of wavelengths that are required for the excitation of popular fluorescent dyes.

"Although the narrow spectral bandwidth (typically

"In order for LED illuminators and light engines to act as a satisfactory replacement for illuminators used in general microscopy applications, such as brightfield illuminators, it is desirable and even necessary to produce white light with characteristics that are similar to the light produced from an incandescent bulb, or in some cases, to accurately replicate the light provided by natural sunlight. This is especially important for microscopy applications that demand high quality light with well-controlled parameters. This is true for human eye viewing, as well as microscope photography and imaging. In a general sense, this means that the LED illuminator or light engine should have a broad spectral response or characteristic that mimics the spectral response of an incandescent bulb, and/or natural sunlight."

In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventor's summary information for this patent application: "One embodiment of the invention is directed to a broad-spectrum, multiple wavelength illuminator for providing light along an optical axis, comprising a luminescent body, and a plurality of semiconductor chips emitting light within one or more wavelength ranges towards the luminescent body, causing the luminescent body to emit light of one or more wavelength ranges, the plurality of semiconductor chips spaced apart from the luminescent body. An optical element adjacent to the luminescent body is used to collect light emitted by the luminescent body. An optical device is used to collect and direct light emitted by the luminescent body and collected by the optical element along the optical axis. Preferably and as an option, an aperture located in the optical axis between the optical element and the optical device passes the light emitted by the luminescent body along the optical axis, wherein light collected by the optical element and the optical device and passed by the aperture forms a beam of light illuminating a target.

"Another embodiment of the invention is directed to a method for providing light along an optical axis, comprising causing a plurality of semiconductor chips to emit light within different wavelength ranges towards a luminescent body spaced apart from the plurality of semiconductor chips, causing the luminescent body to emit light, collecting light emitted by the luminescent body, passing the light collected from the luminescent body through an aperture to form a beam along the optical axis; and collimating the beam and directing the collimated beam along the optical axis to a target.

"Yet another embodiment of the invention is directed to a broad-spectrum, multiple wavelength LED array illuminator for providing light along an optical axis, comprising a substrate and at least one array of multiple LED chips without individual packaging supported by the substrate, wherein the LED chips are distributed laterally with respect to the axis over an area, the LED chips having light emitting surfaces for emitting light in directions transverse to the area. A luminescent layer on at least some of the LED chips emits light in the yellow region of the visible spectrum in response to light emitted by the at least some of the LED chips, and may also emit light in other regions of the visible spectrum. An optical element adjacent to the light emitting surfaces of the LED chips in the at least one array collects and directs light emitted by the LED chips of the at least one array and by the luminescent layer along the axis towards a target, wherein the light received by the target from the optical element is of substantially uniform intensity across a broad spectrum.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 is a representation of the prior art in fluorescence microscopy illumination, showing the major elements of a typical system.

"FIG. 2 is a representation of a prior art illuminator for fluorescence microscopy, using an incandescent bulb as a broad-spectrum light source.

"FIG. 3 is a representation of a prior art illuminator for fluorescence microscopy, using multiple wavelengths of LEDs as the light sources.

"FIG. 4 is a representation of the prior art, showing the spectral profile of an LED-based fluorescence microscopy illuminator providing four specific wavelengths of excitation light.

"FIG. 5 is a representation of the prior art, showing the spectral profiles of an LED light source that is exciting emissions from a luminescent material, such as a phosphor material.

"FIGS. 6A and 6B show two views of one embodiment of an LED array of the present invention, showing the use of multiple LED chips with multiple phosphor types.

"FIGS. 7A and 7B are representations of the spectral profiles of two embodiments of the present invention.

"FIG. 8 shows another embodiment of the present invention, in which the LED excitation light sources are separated in space from the light-emitting phosphors or other luminescent material.

"FIG. 9 shows another embodiment of the present invention, in which VCSEL excitation light sources are separated in space from the light-emitting phosphors or other luminescent material.

"FIG. 10 is a block diagram representation of the illuminator of the present invention and illustrates the different components and their function in the apparatus.

"FIG. 11A is a representation of one embodiment of the present invention using a diffuser plate as a light scrambler/randomizer. FIG. 11B shows a cross-section view of the optical elements of one practical implementation of one embodiment of the present invention.

"FIGS. 12A and 12B show polar and rectangular coordinate plots of the light output of the LED array used in one embodiment of the present invention, including the half-ball lens that sits over the LED array.

"FIG. 12C provides plots of the light uniformity of the beam that exits the optical elements of one embodiment of the present invention, showing the relative effects of different aperture dimensions and different diffusers.

"FIG. 13A is a schematic view of one embodiment where the light coming from the embodiment in FIG. 11 is sent into a zoom lens system to expand or contract the beam width.

"FIG. 13B is a schematic view of another embodiment where a mirror is placed between the embodiment in FIG. 11 and zoom lens system shown in FIG. 13A to redirect the light path.

"FIG. 14 is a schematic view of yet another embodiment of the present invention, using a light mixing tube as a light scrambler/randomizer and the variable distance between the collector lens and tube entrance as a means to change the effective aperture size.

"FIG. 15 is a representation of one embodiment of the present invention that uses a narrow bandpass filter wheel, following the embodiment of FIG. 11, to either select a specific wavelength range, or to further narrow the bandwidth of the selected wavelength range."

URL and more information on this patent application, see: Lee, Ho-Shang. Broad-Spectrum Illuminator for Microscopy Applications, Using the Emissions of Luminescent Materials. Filed November 5, 2013 and posted August 28, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=4600&p=92&f=G&l=50&d=PG01&S1=20140821.PD.&OS=PD/20140821&RS=PD/20140821

Keywords for this news article include: DiCon Fiberoptics, DiCon Fiberoptics Inc., Electronics, Semiconductor.

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Source: Electronics Newsweekly


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