Petitioner: Haag-Streit AG
`Petitioner: Haag-Streit AG
`
`Ex. 10(cid:20)(cid:23)
`
`EX. 1014
`
`

`

`(12) United States Patent
`Us 6,193,401 B1
`(10) Patent N0.:
`Girkin et al.
`(45) Date of Patent:
`Feb. 27, 2001
`
`U8006193401B1
`
`(54) OPTICAL ELEMENT
`
`(56)
`
`References Cited
`
`(75)
`
`Inventors: John Michael Girkin, Dunbartonshre;
`Martin David Dawson, Glasgow, both
`of (GB)
`
`(73) Assignee: University of Strathclyde, Glasgow
`(GB)
`
`U.S. PATENT DOCUMENTS
`
`4,266,534 *
`4,752,123 *
`5,099,399 *
`5,491,765 *
`
`5/1981 Ogawa ..................................... 128/6
`6/1988 Blaker .................................. 351/161
`
`3/1992 Miller etal.
`..
`..... 385/15
`2/1996 Matsumoto ............................ 385/33
`
`FOREIGN PATENT DOCUMENTS
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`0733923 A1
`
`9/1996 (EP) .
`
`* cited by examiner
`
`(21) Appl. No.:
`
`09/367,422
`
`(22) PCT Filed:
`
`Feb. 13, 1998
`
`(86) PCT No.:
`
`PCT/GB98/00326
`
`§ 371 Date:
`
`Aug. 30, 1999
`
`§ 102(e) Date: Aug. 30, 1999
`
`(87) PCT Pub. No.: WO98/36295
`
`PCT Pub. Date: Aug. 20, 1998
`
`(30)
`
`Foreign Application Priority Data
`
`Feb. 15, 1997
`
`(GB)
`
`.................................................. 9703156
`
`(51)
`
`Int. Cl.7 ................................ F21V 7/04; G02B 6/00;
`G09F 13/00
`
`.......................... 362/551; 362/556; 362/560;
`(52) US. Cl.
`362/308; 362/328; 362/555; 385/901; 385/33,
`385/49; 385/93
`(58) Field of Search ..................................... 362/551, 555,
`362/556, 560, 328, 308, 327, 385/900,
`901, 33, 49, 93
`
`Primary Examiner—Sandra O’Shea
`Assistant Examiner—Ali Alavi
`
`(74) Attorney, Agent, or Firm—Alston & Bird LLP
`
`(57)
`
`ABSTRACT
`
`The light emitted by diodes of the Gallium Nitride type
`which comprises two distinguishable emissions is controlled
`by a single optical element (10) in the form of a lens having
`a central part and an annular part with different optical
`powers. The total output light of the diode may be collimated
`or brought to a common focus. The single optical element is
`preferably injection moulded and the annular part takes the
`form of a diffraction lens. The first part (12) is preferably a
`refractive lens which has a different optical power to the
`second part (14)which is preferably a diffractive lens. The
`optical power of the refractive lens (12) (the first optical
`power) and the optical power of the diffractive lens (14) (the
`second optical power) are selected to match the light source
`that the lens (10) is to be used with.
`
`4 Claims, 2 Drawing Sheets
`
`
`
`

`

`U S. Patent
`
`Feb. 27, 2001
`
`Sheet 1 012
`
`US 6,193,401 B1
`
`
`
`10
`
`14
`
`12
`
`O
`
`1
`
`12
`
`14
`
`1h
`
`F1623
`
`FlG.2b
`
`

`

`US. Patent
`
`Feb. 27, 2001
`
`Sheet 2 012
`
`US 6,193,401 B1
`
`
`
`

`

`US 6,193,401 B1
`
`1
`OPTICAL ELEMENT
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates to a single optical element,
`in particular to a lens suitable for use with a particular type
`of light emitting diode (LED) structure.
`
`FIELD OF THE INVENTION
`
`A typical structure of one specific type of LED is shown
`in FIG. 1a. The light emitting material
`is housed in a
`cup-shaped reflector. The light emitted from such an LED
`has two spatial components, as shown in FIG. 1b, one of the
`components (the central component labelled L1) arises from
`direct emission from the top face of the LED, the other (the
`component around the perimeter labelled L2) arises from the
`sides of the LED and is reflected by the cup-shaped reflector.
`These two components are separated by an area with sub-
`stantially no emission (labelled D1) and which although
`illustrated as circular need not be circular. The light L1
`emitted from the top face of the LED typically accounts for
`only about 20% of the total light output.
`The effect of having direct emission from the top surface
`of the LED and indirect (reflected) emission from the sides
`of the LED is that the device appears to have two light
`sources, S1, S2 as shown in FIG. lc. One source (s1) is for
`the direct emission L1 from the top surface;
`the second
`source (s2) is for the indirect emission L2, and appears to be
`behind the LED device. Thus, the second source (s2) is a
`virtual source.
`
`The light pattern from the direct emission L1 is a narrow
`beam of light; whereas the light pattern from the indirect
`emission L2 is an annular beam surrounding and spaced
`from the direct emission. The light emission from the type
`of LED structure shown in FIG. 1, has a highly divergent
`component (the indirect emission) L2 and is spatially inho-
`mogeneous. Thus it is difficult to use this type of LED as an
`effective optical source of collimated or focused light. It will
`also be appreciated that certain forms of conventional lamp
`sources display similar characteristics of spatially inhomo-
`geneous emission.
`
`SUMMARY OF THE INVENTION
`
`It is an object of this invention to obviate or mitigate the
`above disadvantage.
`The general solution to the above problem is to use in
`combination with an LED or other source as previously
`described a single optical element which has two optical
`powers, one of the optical powers is used to focus or
`collimate one component of the LED emission, the other
`optical power is used to focus or collimate the other com-
`ponent of the LED emission; thus the two spatial compo-
`nents of the LED emission can be collimated or brought to
`a common focus.
`
`One advantage of the present invention is that it allows a
`significant proportion of the light emitted from such an LED
`or other source to be focused or collimated onto another
`
`optical element (e.g. a waveguide such as an optical fibre
`which would homogenise the beam profile, or a combiner),
`making this type of LED or other source a convenient light
`source for many optical applications which have previously
`used laser sources.
`
`According to a first aspect of the present invention there
`is provided a single optical element comprising a first part
`with a first optical power and a second part with a second
`
`10
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`15
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`20
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`2
`optical power, where the second part is disposed around the
`perimeter of the first part.
`It will be understood that the single optical element is to
`be used with an optical source such as the previously
`described LED producing both a narrow beam of light and
`an annular beam of light, and one of the parts is used to focus
`or collimate the narrow beam of light and the other part is
`used to focus or collimate the annular beam of light, the first
`and second optical powers being selected to ensure that the
`narrow beam of light and the annular beam of light are
`brought to a common focus or are collimated.
`The first part may be either a refractive or a diffractive
`lens. The second part also may be either a refractive or a
`diffractive lens. It is also preferred that the single optical
`element is manufactured by injection moulding.
`According to a second aspect of the present invention
`there is provided a single optical element according to the
`first aspect of the invention in combination with a light
`source that produces direct and reflected light, where the
`direct light is a narrow beam, and the reflected light is an
`annular beam,
`the combination producing at a common
`focus or in common collimation both direct and reflected
`light.
`According to a third aspect of the present invention there
`is provided an optical system comprising at least two single
`optical elements according to the first aspect of the present
`invention and arranged to produce collimated beams, each
`single optical element being associated with a LED or other
`source as previously described as its input, a combiner to
`combine the output of each optical element, and an output
`lens arranged to focus the combiner output to a common
`focus.
`
`Preferably, each of the LEDs (or other sources) emits light
`of a different colour.
`
`It will be understood that by varying the emission inten-
`sity of each of the coloured LEDs the colour produced at the
`output of the combiner can be varied, thus a specific spectral
`output characteristic can be produced by the system. Alter-
`natively the differently coloured LEDs may be switched on
`in turn for use as part of a scanning system.
`These and other aspects of the invention will become
`apparent from the following description when taken in
`combination with the accompanying drawings in which:
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1a is a sectional view of a known specific type of
`LED device;
`FIG. 1b is a diagrammatic view of the two components of
`light emission from an LED of FIG. 1a;
`FIG. IC is a sectional view of the LED device of FIG. 1a
`
`showing the source (s1) of the direct emission and the
`apparent source (s2) of the indirect emission;
`FIG. 2a schematically shows a front view of a single
`optical element with two parts in accordance with the
`present invention;
`FIG. 2b schematically shows a side view of the single
`optical element of FIG. 2a;
`FIG. 3 shows the optical element of FIG. 2 focusing the
`light emission from an LED to an optical fibre according to
`one aspect of the invention; and
`FIG. 4 shows an optical system for combining the outputs
`of two LEDs using the optical element of FIG. 2 according
`to another aspect of the invention.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`FIG. 1a shows the specific type of LED structure which
`is used in embodiments of the present invention and which
`
`

`

`US 6,193,401 B1
`
`3
`is representative of certain other forms of conventional lamp
`sources. An example of the specific type of LED structure
`which is used in embodiments of the present invention is the
`Gallium Nitride or GaN LED available from Nichia Chemi-
`
`cal Company. This type of LED has a single quantum—well
`emitting—region and it emits light of narrow bandwidth (for
`example 10 nm spectral linewidth) and high power (for
`example several milliwatts). FIG. 1b shows the two com-
`ponents of light emission (L1 and L2) that are characteristic
`of the specific type of LED structure shown in FIG. 1a. lc
`shows the source SI and the apparent source S2 that give
`rise to the two components of light emission of FIG. 1b.
`
`Referring to FIGS. 2a and 2b, which show two views of
`a single optical element,
`the optical element
`is a dual
`focal-length lens 10 which has two integral parts. The first
`part 12 is generally circular and is located at the centre of the
`lens 10, the second part 14 is annular and is disposed around
`the perimeter of the first part 12.
`
`The first part 12 is preferably a refractive lens which has
`a different optical power to the second part 14 which is
`preferably a diffractive lens. The optical power of the
`refractive lens 12 (the first optical power) and the optical
`power of the diffractive lens 14 (the second optical power)
`are selected to match the light source that the lens 10 is to
`be used with, as will be described with reference to FIG. 3.
`
`FIG. 3 shows the lens 10 focusing the light emission from
`an LED 20 into an optical fibre 22 according to one aspect
`of the invention. To achieve maximum coupling of the light
`from the LED 20 into the optical fibre 22 both the spot size
`and the angle (numerical aperture) of the output from the
`lens 10 (the lens output 24) should be matched to the
`aperture of the optical fibre 22. Only the numerical aperture
`needs to be matched in this embodiment because typically
`the spot size is smaller than the aperture of the fibre 22 (and
`of course the product of numerical aperture and spot size is
`invariant).
`
`The required lens magnification (RLM) equals the
`numerical aperture (NA) of the LED divided by the numeri-
`cal aperture (NA) of the optical fibre, as given by equation
`1:
`
`
`LED NA
`_ Fibre NA
`
`RLM
`
`and the required focal length is given by equation 2:
`
`Focal Length:
`
`RLM >1: (Object distance + Image distance)
`(RLM + DZ
`
`(1)
`
`(2)
`
`3
`
`Applying equations 1 and 2 to the embodiment of FIG. 3
`yields equations 3 and 4 for the direct light case (i.e. light
`(L7) emitted from the top face of the LED 20).
` NA
`LED
`NAFIBRE
`
`RLM] =
`
`(
`
`)
`
`d
`d
`RLM]
`Focal length l =w (
`(RLM1+1)2
`
`4
`
`)
`
`Applying equations 1 and 2 to the embodiment of FIG. 3
`yields equations 5 and 6 for the indirect light case (i.e. light
`(L2) emitted from the sides of the LED then the reflector):
`
`RZMZ =
`
` ALED
`NAFIBRE
`
`Focal length 2 =
`
`RLM2* (d1 + XLED + xWD + d3)
`(RLMZ + 1)2
`
`(5)
`
`(6)
`
`Typical values for the parameters in equations 1 to 6 are
`given in Table 1 for a GaN LED. Using equations 3 to 6 with
`values of the desired distance from the LED 20 to the lens
`
`10
`
`10 and the desired distance from the lens 10 to the optical
`fibre 22, the required values of the first optical power and the
`second optical power can be calculated. Optical power, of
`course, is the inverse of focal length.
`FIG. 4 shows an optical system 30 for combining the
`outputs of two LEDs according to another aspect of the
`invention. The system 30 has a first LED 20a with a
`corresponding first lens 10a, and a second LED 20b with a
`corresponding second lens 10b. The output of the first lens
`(the first lens output 24a) and the output of the second lens
`(the second lens output 24b) are both collimated beams.
`These collimated beams are input to a combiner 40 which
`transmits the second lens output 24b and reflects the first
`lens output 24a to produce a collimated output 42 which is
`a combination of the first and second lens outputs 24a,b and
`which is delivered to an output lens 10C, preferably an
`achromatic lens, arranged to focus the combined lens out-
`puts 42 into the optical fibre 22. Lens 106 may be a singlet
`or may be multi-element and is a single focal length lens.
`Additional lenses may be included, for example, in the path
`of the first lens output 24a or in the path of the second lens
`output 24b. Thus diffraction gratings or dichroic mirrors
`may be used to combine the emission from several LEDs.
`The two LEDs (20a, 20b) emit
`light at different
`wavelengths, for example,
`the first LED 20a preferably
`emits red light, the second LED 20b preferably emits blue
`light so that by varying the emission intensity of the LEDs,
`20a and 20b (by individual controllers, not shown) the
`colour produced at the output of the combiner 40 can be
`varied.
`
`Various changes may be made to the above described
`embodiments within the scope of the present invention. For
`example, the first part 12 in the lens 10 need not be circular,
`it may be elliptical or some other shape. This may be
`required if the LED 20 emits a narrow beam which is
`elliptical or some other shape. Similarly, the second part 14
`need not be circular along its outer periphery,
`it may be
`another shape, for example to fit a particular lens holder. The
`first part may not be a refractive lens, it may be a diffractive
`lens. Similarly, the second part may not be a diffractive lens,
`it may be a refractive lens.
`In other embodiments of the optical system 30, more than
`two LED’s may be used. For example, a green LED may
`also be used so that there are red, green and blue LEDs,
`which are the primary colours, and the system may include
`means of adjusting the emission intensity of each of the
`LEDs to produce a collimated output 42 with controllable
`spectral characteristics. Thus a specific spectral output char-
`acteristic can be selected by adjusting the emission intensity
`of each of the LEDs. This can be achieved by increasing or
`decreasing the drive voltage or current of each individual
`LED to make the emission from that LED more or less
`
`intense. In other embodiments of the optical system 30, the
`two LEDs may not emit red and blue light, they may emit
`light of other wavelengths (including infrared).
`In other embodiments of the invention an array of LEDs,
`each of which emits blue light,
`is used to cure dental
`
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`

`

`US 6,193,401 B1
`
`5
`composite material. Aholographic diffusing material may be
`used in combination with the lens 10 to produce a homog-
`enous light distribution which provides uniform curing of
`the dental composite material.
`In other embodiments of the invention an array of
`coloured LEDs may be used for applications such as bio-
`medical imaging, cytology, time-resolved fluorescence, and
`microscopy applications such as fluorescence microscopy.
`
`NALED =
`DIALED =
`NAFIBRE =
`DIAFIBRE =
`NALED2 =
`DIALEDZ =
`XLED =
`XIND =
`
`TABLE 1
`
`0.12 (Direct LED NA)
`0.23 mm (LED Direct Diameter)
`0.37 (Typical Fibre NA)
`0.50 mm (Typical Fibre Core Diameter)
`0.20 (Indirect LED NA)
`0.30 mm (LED Indirect Diameter)
`12 mm (LED to Focus of Output)
`13 mm (Emitting Point Behind LED)
`
`What is claimed is:
`1. The combination of an LED and a single optical
`element, wherein the LED comprises light emitting material
`housed in a cup-shaped reflector, the light emitting material
`having a single quantum-well emitting region such that the
`light emitted from the LED has a first spatial component
`arising from direct emission from the top face of the LED
`which is a narrow beam (L1) and a second spatial compo-
`nent arising from the sides of the LED and reflected by the
`cup-shaped reflector which is an annular beam (L2) and
`
`6
`
`apparently emanating from a virtual source (S2) behind the
`LED, and wherein the single optical element consists essen-
`tially of a first part (12) in the form of a refractive lens with
`a first optical power and a second part (14) in the form of a
`diffractive lens with a second optical power, the second part
`(14) being disposed around the periphery of the first part
`(12), and the arrangement being such that the combination
`delivers the direct and reflected beams at a common focus or
`in common collimation.
`
`2. The combination of claim 1, wherein the LED is a
`Gallium Nitride LED.
`
`3. The combination of claim 1 or claim 2, wherein the
`light from the LED is focussed to a common focus, includ-
`ing an optical fibre (22) arranged to receive the focussed
`light at the fibre input.
`two of the
`least
`4. An optical system comprising at
`combinations claimed in claim 1 or claim 2 and wherein the
`
`light from each LED is collimated, a combiner (40) being
`disposed to combine the two collimated beams, an output
`lens (10c) being arranged to focus the combiner output to a
`common focus, and the emission intensity of each LED
`being controlled by an individual controller which varies the
`drive voltage or current of the LED to produce a desired
`light characteristic at the common focus.
`
`5
`
`10
`
`15
`
`20
`
`25
`
`