Optical element

Details Optical element Optical element

1999-08-30

2001-02-27

O'Shea, Sandra (Department: 2875)

Illumination

Light fiber, rod, or pipe

C362S556000, C362S560000, C362S308000, C362S328000, C362S555000, C385S901000, C385S033000, C385S049000, C385S093000

Reexamination Certificate

active

06193401

ABSTRACT:

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. 1
a
. 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. 1
b
, one of the components (the central component labelled L
1
) arises from direct emission from the top face of the LED, the other (the component around the perimeter labelled L
2
) arises from the sides of the LED and is reflected by the cup-shaped reflector. These two components are separated by an area with substantially no emission (labelled D
1
) and which although illustrated as circular need not be circular. The light L
1
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, S
1
, S
2
as shown in
FIG. 1
c
. One source (s
1
) is for the direct emission L
1
from the top surface; the second source (s
2
) is for the indirect emission L
2
, and appears to be behind the LED device. Thus, the second source (s
2
) is a virtual source.
The light pattern from the direct emission L
1
is a narrow beam of light; whereas the light pattern from the indirect emission L
2
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) L
2
and is spatially inhomogeneous. 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 inhomogeneous 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 component of the LED emission; thus the two spatial components 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 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 intensity 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. Alternatively 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:


REFERENCES:
patent: 4266534 (1981-05-01), Ogawa
patent: 4752123 (1988-06-01), Blaker
patent: 5099399 (1992-03-01), Miller et al.
patent: 5491765 (1996-02-01), Matsumoto
patent: 0733923 A1 (1996-09-01), None

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