WO2014081298A2

WO2014081298A2 - Broad spectrum led and laser based light engine

Info

Publication number: WO2014081298A2
Application number: PCT/NL2013/050845
Authority: WO
Inventors: Richard Johannes Cornelis MEESTER
Original assignee: Quest Photonic Devices B.V.
Priority date: 2012-11-22
Filing date: 2013-11-22
Publication date: 2014-05-30
Also published as: NL2009862C2; WO2014081298A3

Abstract

The invention provides a light engine (54, 54') for a medical device, comprising -a plurality of light sources (41), -a plurality of optical fiber bundles (51, 52); wherein each of the plurality of light source is butt-coupled or otherwise coupled to at an optical fiber bundle (51, 52), so that the optical fiber bundle receives light from the light source to which it is coupled. The light sources (41) can comprise light emitting diodes, LEDs, and lasers, in particular laser diodes. The light engine may comprise at least two groups of light sources, each group emitting a specific spectrum. The first group emits light with a visible light spectrum and the second group emits light with the excitation spectrum of a fluorescence agent.

Description

Broad spectrum LED and laser based light engine

Field of the invention [0001] The invention relates to a light engine or illuminator, in particular to a light engine for use with a medical device such as an endoscope or a laparoscope, more in particular to a light engine for use in the field of molecular and real time fluorescence imaging. Background of the invention

[0002] . A known light engine 10 is shown in figure 1. The light engine comprises two light emitting diodes (LEDs) as light sources, a blue LED 16 and green LED 17. The blue LED 16 has a spectrum 16a with a peak near 400 nm, while the spectrum 17a of the green LED 17 has a peak near 550 nm.

[0003] At least part of the light from LED 16 is collected by lens 13 and transmitted as a more or less parallel blue beam towards reflective surface 1 1 , which bends the blue beam in a second direction. In the path of the blue beam, a second surface 12 in the form of a dichroic mirror is provided. The dichroic mirror is prepared so that it is transparent for blue light but, at least on one side, reflecting for green light. The green light from the green LED 17 is collected by a second lens 15 and transmitted as a more or less parallel green beam towards the second surface 12. The second surface 12 reflects the green beam into the second direction, so that it coincides with the blue beam that travels through second surface 12. The combined beam is collected by a third lens 15, which focuses the light into the entrance of optical fiber bundle 18. The light in the fiber bundle thus has the combined spectrum 19 of light sources 13 and 14. A known light engine is described in published US patent application 2012 / 0 230 024 A1. .Another light engine, using red, green, and blue LEDs connected to respective optical fiber bundles is disclosed in JP 2006-314 686. Fibers from the various optical fiber bundles are mixed with each other, so that effectively a mixture of the incident red, green, and blue light is emitted at a distal end of the fibre bundles.

[0004] Light engines are for example used in medical applications such as fluorescence endoscopy, where the light from the light engine may be used to excite the fluorescence agent and or to illuminate the surroundings for recording a visible light image. Until recently, LEDs were not commonly used. A big drawback of LED- based light engines is that this technology is strongly dependent on the availability of high power LEDS. This holds especially for fluorescent imaging applications where high power light of a particular wavelength is required to generate fluorescence. Combined with the endoscopic transportation of light, i.e. the longer required distance between illuminated object and camera system where losses are high, known LED light engines are just barely capable of illuminating the object sufficiently.

[0005] Other applications for a light engine include machine vision multispectral imaging applications where besides a broad spectrum, high power light engine is required, along with the ability to have multiple specific narrow band wavelengths used for illumination. Commonly used light sources are based on high power halogen lamps coupled into an external fiber bundle. A further requirement of these light engines is a large broad spectrum of light to generate white light. This requires the output light wavelength curve to be as evenly distributed as possible (figure 1 b) with excitation wavelengths having a very narrow peak and high power (figure 1 c). A combination output of the light engine would be the combination of the 2 spectra (figure 1 d).

[0006] The known light engine of figure 1 has a further drawbacks. For one, as shown schematically in figure 2, only a part 22 of the total emitted light by LED 16 is collected in lens 13. LEDs have a very broad angle of light dispersion, hence only a small portion of the available light is used. The light emitted to the side 21 , 23 is not transported to the optical fiber bundle and hence lost. Furthermore, high power LEDs have a relative narrow wavelength over which they transmit the light. This makes it hard to generate an evenly distributed output power light spectrum (as in figure 1 b) and is usually more similar to figure 1 e, where the peaks of each of the primary LED colours is clearly distinguishable. One could use recently developed high power white light LEDs to overcome this problem, however in this case the total power of the white light (from 400 to 650 nm) is less than an LED of a particular colour. Therefore, a 3 LED (RGB white ) light engine has more power than a single white LED light engine. However, a known 3 LED light engine requires two dichroic mirrors 12, which adds to the complexity.

[0007] Figure 3 schematically shows the wavelength-dependent reflective properties of the second surface 12 (dichroic mirror). Known materials have a transition range 32 which is typically 5 - 15 nm wide. For wavelengths in the range 33 the surface is reflecting, in area 31 the surface is transparent. Because a dichroic mirror is for a given wavelength, either reflecting or transmitting, such a dichroic mirror does not allow doubling of the light intensity by providing light sources having the same spectrum in the arrangement of figure 1 (i.e. using multiple white LEDs as described above). If the intensity is to be increased, then sources are placed next to each other. However, due to the limited size of collecting lens (see e.g. lens 13 in figure 2) this typically results in relatively large light losses. Because dichroic mirrors have a slope between turning from transmittive to reflective and steep slopes of < 15 nm are not possible there is a limit to the amount of LED wavelengths one can combine into the light engine. Currently LEDs must be apart at least 20nm or more in order to have a useful addition in terms of light efficiency in these types of light engines. It is therefore an object of this invention to provide an improved light engine which overcomes at least one of these drawbacks. I n particular it is an object of this invention to provide an improved light engine for (medical) fluorescence applications, in particular fluorescence endoscopy or laparoscopy. Summary of the invention

[0008] The invention provides a light engine comprising a plurality of light sources and a plurality of optical fiber bundles, wherein each of the plurality of light source is butt-coupled or otherwise coupled to at an optical fiber bundle, so that the optical fiber bundle receives light from the light source to which it is coupled. The optical fiber bundle may receive only light from a light source to which it is coupled. The optical fiber bundles may be combined in an optical cable. The light engine may be adapted for use in a medical application.

[0009] It is understood that the term "optical fiber bundle" or "fiber bundle" as used in this application indicates a bundle of optical fibers that act as a logical unit. The term "optical fiber cable" is understood as a collection of optical fiber bundles. An optical fiber cable may be a loose connection of fiber bundles, for example without a protective tube. Unless otherwise indicated, an (logical) optical fiber bundle is meant to be provided with a single light source input, i.e. all fibers in the optical fiber bundle will receive the same type of light. An optical fiber cable may comprise fiber bundles for various types of light.

[0010] Each light source is (butt-)coupled to at least one fiber bundle. A plurality of light sources may be used, wherein each light source is butt-coupled or otherwise coupled to at least one fiber bundle. The at least one fiber coupled to each light source are combined in a fiber bundle. I n an embodiment, all fibers of the fiber bundle are (butt-)coupled to exactly one light source of the light engine. The fiber bundle may be provided with means for mixing the light from the various at least one fibers coupled to distinct light sources.

[0011] I n an embodiment according the invention, the light sources comprise light emitting diodes, LEDs.

[0012] LEDs can be advantageously butt-coupled to a fiber bundle. Typical LEDs have an advantageous Numerical Aperture (NA) for coupling with a fiber bundle.

[0013] I n an embodiment according the invention, the light sources comprise lasers, in particular laser diodes. In a further embodiment, the one or more lasers or laser diodes are each provided with a lens for shaping the emitted laser beam. The assembly of laser (diode) with lens is then, as a light source, coupled or butt-coupled to the fiber bundle. I n an advantageous embodiment, the laser beam is shaped with the lens (before being coupled to the fiber bundles) in order to match the Numerical Aperture (NA) of other light sources, such as LEDs which may be simultaneously used in the light engine. The NA of the laser may be enlarged so that the laser spot covers a larger area of the fiber bundle entrance. The larger laser spot is safer, so that the laser safety in increased. If the light from the laser is mixed in the light engine, the emitted light is also distributed over a large spot/area so that also at the light exit of the light engine the laser safety is increased. Use of a lens thus reduces laser safety requirements, making handling of the light engine easier and less expensive. In other words, the matching (e.g. enlarging) of the NA allows for improved laser power requirements without exceeding the laser safety levels human can use without laser glasses. By using a lens and coupling with the fiber bundle, a higher-class laser device may be used without increasing the laser safety requirements. The use of the lens effectively reduces the danger, while still allowing the generated laser power to be used in the application.

[0014] I n an embodiment according the invention, the light engine comprises a first group of light sources emitting a first spectrum and a second group of light sources emitting a second spectrum, said first and second spectrum being substantially different. It is noted that a group of light sources can also consist of one or more light sources. This embodiment advantageously allows to mix various types of light sources, each light source being optimized for a specific purpose. Light sources of the first group may be optimized for efficient generation of broad-band visible light, while light sources of the second group may be optimized for generating narrowband (high power) light with a very stable and predictable power output. Prior art light engines typically rely on the use of one specific broad-band light source and the use of filters to shape the spectrum. The single broad-band light source is typically not as efficient and well-calibrated as a collection of specialized light sources, particularly a collection comprising both broad-band and narrow-band sources as well as are not able to combine additional high power narrow band light sources in the same optical path at a predefined Numerical Aperture. Spectral mixing of multiple high power light sources matched with a camera system specifically designed to unscramble the multiple fluorescence signals returned as a result of the multiple excitation sources are made possible by this configuration.

[0015] The first spectrum may be a broad visible light spectrum, for illuminating an environment so that the environment can be recorded and displayed for e.g. real- time applications. The second spectrum may be an excitation spectrum of a fluorescence agent. The first spectrum may be broader than the second spectrum. The first spectrum may overlap the entire second spectrum. The first spectrum may be selected or modified (e.g. through a filtering module) to exclude the fluorescence emission wavelengths of the fluorescence agent. By filtering the fluorescence radiation from at least the visible light emitted by the light engine, the detection of fluorescence radiation can be improved. After all, the background signal detected by the fluorescence detector (e.g. a camera) caused by the broad-band visible light has been strongly reduced or removed altogether. Generally the excitation radiation has a narrow bandwidth profile, so that filtering the excitation radiation is not required. However, if the second (excitation) radiation spectrum overlaps the fluorescence spectrum, the second spectrum can be filtered as well. I n any event, the most convenient way of filtering may be to filter after the light from the first and second group of light sources has been mixed. In that case, both spectra are simultaneously filtered. This can for example be achieved by first guiding the light through a mixing module and then through the filtering module.

[0016] In an embodiment according the invention, the light engine is further provided with a filtering module for filtering light as described above, said filtering module receiving light from at least one fiber bundle and directing said light through a filtering device so that, depending on the wavelength of the light, a part of the light is transmitted through to an outgoing fiber bundle and another part of the light is redirected to an absorbing surface.

[0017] In an embodiment according the invention, the light engine is further provided with a mixing module, said mixing module comprising an enclosure connected to a plurality of incoming fiber bundles and at least one outgoing fiber bundle, said fiber incoming and outgoing fiber bundles having respective terminal faces opposite each other. [0018] I n such a mixing module, the input fiber bundles may each carry light with a distinct spectrum, but the outgoing fiber bundle(s) will each carry light with the same, mixed, spectrum.

[0019] I n an embodiment according the invention, the terminal face of an outgoing fiber bundle is provided with a diffusing layer.

[0020] Such a layer improves mixing of the incoming light.

[0021] In an embodiment according the invention, the light engine is further provided with a attenuation module, said attenuation module comprising an enclosure connected to an incoming fiber bundle and an outgoing fiber bundle, said fiber bundles having terminal faces opposite each other, and means for adjusting the distance between the terminal faces.

[0022] With an attenuation module, the power of light can be (continuously) adapted to conform to the application's requirements. E.g. for endoscopic applications typically less light is needed than for other applications.

[0023] I n an embodiment according the invention, the light engine further comprises absorbing material surrounding the incoming fiber bundle.

[0024] I n an embodiment according the invention, the light engine comprises an active cooling component, such as a Peltier element, for cooling at least one of the light sources; and control electronics for measuring and controlling the temperature of the at least light source in order to minimize wavelength shift of the light source light.

[0025] Minimizing temperature variations helps to stabilize the spectrum of light sources, making quantitative applications possible, such as quantitative fluorescence applications.

[0026] I n an embodiment according the invention, the output light power is controllable and stable for allowing quantitative measurements in fluorescent image guided surgery.

[0027] The invention further provides a system of a light engine as described above and a (multispectral) camera, wherein the light engine is adapted to control the emitted light in dependence of the camera exposure time. The light engine can comprise a controller which is programmed with a light source sequence program that has a closed feedback loop with a multispectral camera for control of the light in relation to the camera exposure time. The feedback loop can be implemented as follows. The camera (the radiation detector) is configured to monitor the fluorescence radiation on a first detection channel and the excitation radiation (also known as the "second spectrum" light) on a second channel, and the controller is configured to control the light sources of the light engine in dependence of both signals. That way the excitation intensity can be varied as a function of the detected radiation. I n addition, the camera exposure time can be varied as a function of excitation and fluorescence radiation. By adjusting these parameters, a point may be found with a strong fluorescence signal which, however, does not saturate the detectors. That way, a light engine settings for optimal fluorescence detection sensitivity or signal/noise ratio can be found.

[0028] The invention further provides a system of a light engine as described above and a ring light adapted to receive light from the light engine via at least one fiber bundle, wherein the light ring comprises a ring with light distributing elements, wherein each light distributing element is connected to at least one fiber from the at least one fiber bundle.

[0029] Such a ring light, connected to a light engine according the invention, can spread an even spectrum, without shades or reflections that cause problems with interpretation of light measurements (such as in fluorescence applications).

[0030] I n an embodiment according the invention, a plurality of light engines are connected to an optical fiber cable, each light engine providing light to at least one fiber bundle of the optical fiber cable.

[0031] I n an embodiment according the invention, the system comprises an imaging system for fluorescence imaging, wherein the light engine is adapted to provide light comprising light at a visible wavelength, light at an excitation wavelength of a fluorescence agent, but excludes light at a fluorescence wavelength of the fluorescence agent. The imaging system is adapted to detect reflected light at the visible wavelength and light at a fluorescence wavelength coming from the fluorescence agent.

[0032] The invention provides a system of a light engine as described above and a connected laparoscope.

[0033] The invention also provides a light engine which allows combination of light with the same wavelength as well as combining LEDs which are from the same colour but different colour bins (colour bins are manufacturing controlled peak LED wavelengths which are very close together (usually +-5nm per bin).

[0034] The invention provides a ring light for use with light engine to deliver all power in the fiber bundle(s) onto an object by dividing the total fiber bundle(s) up into smaller fibers or new, mixed, fiber bundles and placing them evenly spaced around a lens system used by an imaging device.

[0035] The invention further provides a system of a light engine and a laparoscope. [0036] The invention further provides a system comprising a light engine combined with an imaging system, a lens and a ring light, for use in fluorescence imaging and real time image guided surgery.

[0037] The imaging system is used for visualizing fluorescent chemicals inside the tissue, either targeted probes or a contrast agent probe, where the light engine is programmed to provide the right power of light and of the right wavelength of light to provide the required optical "white light" for visualization as well as the required amount of a (one or more) specific wavelength of light which are specifically linked to be the excitation wavelength of the fluorescent probe(s) such that the probe(s) start emitting light at a different wavelength of light. The light engine does not provide light of this particular emitting wavelength (e.g. by carefully selecting the light sources and/or by employing a filtering module to filter out the fluorescence wavelengths) and the camera is capable of detecting this particular emitting wavelength.

[0038] The invention provides a system of a light engine and a (multispectral) camera system, with a programmable connection, or feedback loop, between the camera system and at least one light source of the light engine, wherein said at least one light source is controllable by the camera system. The control can comprise on/off control, power control, wavelength control (in case of a tunable light source) , etc.

[0039] According to an aspect of the invention, each or at least one of the light sources of a light engine can be controlled in intensity and on/off state. This allows the light engine to create internal "programs" of light sources being switched on/off or intensity controlled in time. This allows, when coupling and synchronizing the light engine to a camera system to synchronize the output of light to the frame time and exposure time of the camera system creating a real time feedback loop between camera and light source, the light engine to control the amount and wavelength of light hitting the object of interest and enables fine-grained control of the light for the application to make sure that certain wavelengths of light are disabled such that they don't reach the camera by means of reflection, which is important in multispectral imaging or fluorescent imaging. Standard light engines can only achieve this possibility by placing filters inside the light engine at production time and have as such no real-time control over the light source. Multispectral unmixing is one of the features that is enabled by having real time control over the light sources and intensity. [0040] A light engine according the invention may be used in any of the applications mentioned in the description of the background part of the invention.

[0041] I n an earlier patent application filed on July 5, 2012 with the Dutch Patent Office and having the application number N2009124 by the same applicant, a method for detecting fluorescence radiation from a fluorescence agent is disclosed. The method comprises

- emitting light at an excitation wavelength range for causing fluorescence radiation emission in the fluorescence agent, said fluorescence radiation having a

fluorescence wavelength profile;

- detecting light at a first fluorescence wavelength range as a first detection signal;

- detecting light at a second fluorescence wavelength range as a second detection signal;

- numerically determining a third detection signal with an improved fluorescence-to- background radiation ratio based on the first detection signal, the second detection signal, and the fluorescence wavelength profile.

[0042] By measuring at two different fluorescence wavelength ranges, and using knowledge of the fluorescence emission distribution curve at least in those ranges, the influence from the background radiation to the measured signal can be numerically reduced or practically eliminated. Thus, the signal to noise (fluorescence-to-background) ratio is advantageously improved.

[0043] The above described method, or any of the variants described in the above mentioned application, can be advantageously embodied using a light engine as described in the present application. Such combinations are thus explicitly disclosed by reference to the corresponding parts of the earlier application.

[0044] I n an earlier Dutch patent application, N2009021 , filed June 18, 2012, the applicant discloses a method of creating a dichroic prism assembly for use as a light separation device in an endoscope tip. The method comprises providing a dichroic prism assembly module comprising a plurality of prisms bonded together. The module extends along a longitudinal axis, the module having length L1 , the module having a width W along a lateral axis and a height H along a height axis, wherein the width W and height H are sufficiently small for use in an endoscope. The module is cut so that a dichroic prism assembly is formed having a second longitudinal length L2, so that the formed dichroic prism assembly is suitable for use in an endoscope. The module may be cut in at least two parts, wherein the cutting plane is essentially perpendicular to the longitudinal axis and parallel to the lateral axis and height axis. [0045] That application also discloses also provides a measurement device for measuring fluorescence radiation from a fluorescence agent having a fluorescence wavelength profile, the device comprising a wavelength separation device configured to receive incident light originating from the agent and to separate said light into a plurality of channels; at least two imaging sensors connected to at least two respective channels of the plurality of channels, wherein the first channel is configured for transmitting light at a first fluorescence wavelength range, from which the respective sensor will generate a first detection signal, and the second channel is configured for light at a second fluorescence wavelength range, from which the respective sensor will generate a second detection signal; a processing device configured for numerically determining a third detection signal with an improved fluorescence-to-background radiation ratio based on the first detection signal, the second detection signal, and the fluorescence wavelength profile.

[0046] The light engine according the present invention may be advantageously used in combination with a dichroic prism tip and/or fluorescence application as disclosed in the above-mentioned earlier application. Such combinations are thus explicitly disclosed by reference to the corresponding parts of the earlier application.

Brief description of the Figures

[0047] On the attached drawing sheets,

• figure 1 a-e schematically shows a known light engine and exemplary light engine spectra;

• figure 2 schematically shows a detail of a known light engine;

· figure 3 schematically shows a wavelength dependence of a surface;

• figures 4a-4d schematically show an LED for use in a light engine according to an embodiment of the invention with various coupling means;

• figures 5a-5d schematically show fiber bundles and cables for use in a light engine according to an embodiment of the invention and various couplings of fiber bundles with light sources;

• figure 6 schematically shows a filter module according to an embodiment of the invention;

• figure 7 schematically shows a mixing module according to an embodiment of the invention;

· figure 8 schematically shows a attenuation module according to an embodiment of the invention; • figure 9 schematically shows a light engine system according to an embodiment of the invention;

• figures 10a-b schematically shows spectra in a light engine according to the invention; and

· figure 1 1 schematically shows a ring light connected to light engines according to an embodiment of the invention.

Detailed description [0048] Figures 1 -3 have been described in the introduction.

[0049] Figure 4a schematically shows an LED board 40 with four LED dies 41 . In figure 4b, the LED dies (not shown) are butt-coupled to optical fiber bundle 42. I n the butt-coupled arrangement of figure 4b, the LED die is essentially comprised in or against the optical fiber bundle, so that effectively all light emitted by the LED enters the fibers of the fiber bundle. As such, a very high efficiency of light transfer from the LEDs to the fiber bundle is obtained. I n the example of figures 4a and 4b, four LED dies are butt-coupled into the same optical fiber bundle. However, depending on the diameters of the LED dies and the optical fiber, any number of dies can be butt- coupled into the same fiber bundle.

[0050] Figure 4c shows a variant where an LED with a lens 43 is used, and the fiber bundle 44 is butt-coupled to the lens 43 of the LED instead of the die. The entrance to the fiber bundle 44 is thus very close to the lens 43, so that a maximum amount of light is coupled into the fiber bundle 44.

[0051] Furthermore, as shown in figure 4d, a parabolic reflector 45 or similar construction can be build around the lens 43 such that the focus position of the parabolic reflector focuses most of the led power into the fiber bundle 44. Since at the optical axis of the lens 43, most of the LED power is at a low angle (< ± 10 degrees) a large portion of this light enters the fiber bundle 44.

[0052] I n all embodiments, large Numerical Aperture (NA) fibers like broscilicate fibers, which advantageously allow light entering the fiber at wide angles, may be used in the fiber bundles.

[0053] Figure 5a shows an optical fiber cable 50 with inner fiber bundles 52 and outer fibers bundles 51 in a ring-like setup, the inner fiber bundles 52 having a smaller diameter than the outer fiber bundles 51 . The fiber bundles are build up of smaller fibers creating a "logical" bundle, wherein each smaller fiber typically receives the same wavelength of light. Multiple configurations of larger and smaller fiber bundles can be used to construct the final fiber cable and different stacking forms can be used like hexagons, random distribution, or others to provide the best efficiency.

[0054] Figure 5b shows the combined fiber cable 50 of figure 5a with attached to it a light module, in the current example an LED module 53. The light module 53 with the attached fiber cable 50 can be said to form a light engine 54, outputting the produced light through the fiber cable. The LED module 53 comprises a number of LED dies or LEDs with lenses, with each LED or lens butt-coupled to one of the fibers bundles 51 , 52 of the combined fiber 50. The light from the LED dies or LED with lens is thus efficiently coupled into the fiber bundles 51 , 52 of the combined optical fiber cable 50.

[0055] As illustrated in figure 5d, besides LEDs coupled into the fiber bundle, also solid state laser modules 56 can be coupled efficiently into a fiber bundle through either butt-coupling or a lens construction. Since lasers are a coherent light source, lasers can be coupled into fiber bundles either through butt-coupling (small fiber bundles) or through a lens system. Depending on the application either one or the other can be used. For effective coupling of light from a light source into fibers of a fiber bundle, it is advantageous to have the angle of the light adjusted when it outputs the light source, such that a larger field is illuminated. Therefore, the parallel laser beam enters a lens 57 just before it is coupled into a fiber bundle 58 such that the light is divergent and hence leaves the fibers of the bundle at the same angles.

[0056] A light engine can thus also combine LED and laser light sources.

[0057] Furthermore the one or more fiber bundles output from each of multiple LED or laser based light engines 54 can be bundled together into one larger fiber cable 55. This is schematically illustrated in figure 5c. The assembly of three light engines 54 and the beginning of cable 55 thus form a combined light engine 54'.

[0058] The fiber cable 55 receives fiber bundles 59a, 59b, 59c from respective light engines 54. In an embodiment, outgoing fiber bundles 59d, 59e, 59f are each comprised of fibers from all incoming fiber bundles 59a, 59b, 59c. That way, the incoming light is uniformly mixed in the outgoing fiber bundles 59d, 59e, 59f.

[0059] I n an embodiment, a plurality of dies or lenses is butt-coupled to the same optic fiber bundle 51 , 52. In general: a plurality of dies (or lasers) that all emit light at the same wavelengths can be considered as forming a single light source. I n an alternative embodiment, one die or lens is butt-coupled to precisely one optic fiber bundle 51 , 52. [0060] Different LED dies can be provided in the LED module 53. For example, green and blue LEDs can be provided so that some fiber bundles receive green light and others receive blue light.

[0061] I n an embodiment where laser sources and LEDs are combined; for example using LEDs to provide light to the large fiber bundles 51 on the outside and lasers to provide light to the fiber bundles 52 forming a centre ring light.

[0062] All LEDs and lasers can be individually controlled or by pairs, whichever is appropriate to better control the temperature (this depends on the used source).

[0063] Because, unlike the prior art light engine described in the introduction, a light engine according the invention makes it possible to easily combine multiple LEDs and/or lasers, the LEDs and/or lasers themselves can be run at lower power, resulting in less generated heat and less output light wavelengths shifts caused by increasing heat, yielding a more wavelength stable light source. A feedback loop with electronics for controlling the temperature and keeping the light sources at a stable temperature is provided in this light engine.

[0064] When all fiber bundles 51 , 52 are integrated into the bigger fiber cable 65, an extra filtering module 60, shown schematically in figure 6, can be added to remove light at unwanted wavelengths or frequencies from the bundle. The filtering module 60 is connected to at least one input fiber bundle 65 for receiving light therefrom and to at least one output fiber bundle 66 for outputting light. The incoming light is focused by lens 61 into a parallel beam which is directed to a dichroic mirror 63. The dichroic mirror selectively transmits some of the light (depending on wavelength) and reflects other parts of the spectrum. The transmitted light is collected by a second lens 62 and focussed onto the entrance of the output fiber bundle 66. The reflected light is discarded, for example by directing it to an absorbing sink 64. Depending on the transmitting and reflecting properties of the dichroic mirror 63, a part of the spectrum of the light will be removed.

[0065] Such removal of a part of the spectrum can be employed to remove .e.g. fluorescence emission wavelengths from broad-spectrum (white light) input light.

[0066] Figure 7 schematically shows a mixing module 70. The mixing module 70 is connected to an incoming fiber cable 71 , comprising (in the present example) three fiber bundles 73a, 73b, 73c for incoming red, green, and blue light. The module 70 is also connected to outgoing fiber cable 72, in this example also comprising three bundles 74a, 74b, 74c. Between the terminal surfaces of the incoming cable 71 and the outgoing cable 72 an enclosed space with reflecting sides is provided. I n this space, the light can mix, so that the light that is received by the outgoing bundle is a mixture of the incoming light. That is, in the present example a white mixture of the red, green, and blue incident light is transmitted by the bundles of outgoing cable 72.

[0067] I n an embodiment, the outgoing fiber cable 72 is provided, at its incident surface, with a diffusing layer 75 accepting light from all angles which further helps the mixing of the light.

[0068] Figure 8 schematically shows an attenuator module 80 for use with a light engine according the invention. Light from the incoming fiber cable 85 is received in enclosure 80 which has an adjustable width w, the width w being the distance between the terminal surfaces of incoming fiber cable 85 and the outgoing fiber cable 86. A part of the light from the incoming fibers 85 will directly fall on the terminal surface of outgoing fibers 86 and will thus be transmitted further. Another part is reflected by reflecting surface 83, 84 surrounding the terminal surface of outgoing fiber 86. The incoming fiber is surrounded by absorbing material 81 . The reflected light that falls on the absorbing material 81 will be absorbed and is thus discarded. As such, the module brings a portion of the incoming light to the outgoing fiber 86. The portion is dependent on the adjustable width w and decreases with increasing w.

[0069] Using an attenuator module 80, the intensity of light of the light engine can be quickly and easily varied, without directly adjusting the power supply to the light sources. Some light sources may have adjustable power or may exhibit undesirable properties (hysteresis effects, color shifting, etc) when the power is dynamically controlled. For such light sources, the attenuation module 80 is particularly suitable.

[0070] Figure 9 shows a light engine 53, 50 connected to a number of light adapting modules 60, 70, 80, finally delivering the light to a medical device 90, such as an laparoscope, an endoscope or a device using an external ring light. For example, if the endoscope is used, an attenuator module 80 may be used to limit the amount of light transmitted, whereas for use in a ring light, all available light may be used and the attenuator module 80 is not required. A ring light can thus be directly connected to a light engine 53, 50.

[0071] Returning to figure 5c, using a configuration comprising a number of light engines and combining the output of the light engines in a randomly distributed fiber bundles 59d, 59e, 59f has an added benefit that a ring light connected to this light engine is able to distribute light with all input wavelengths onto the object in an even and evenly distributed way. The even distribution can be optionally improved by using a mixing module 70. [0072] Using an evenly distributed "flat" light source allows to light a subject with flat, evenly distributed light, allowing for more precise calculations and no non-uniform light distribution effects. When combined with a light distribution device such as a light ring, it is possible to also prevent shading effects such as caused when light comes from one spot. Light sources and devices having an unevenly distributed field of light, such as from a prior art light engine, introduce complexity and errors in calculations, may show up as color rings and bright spots, and may provide shading and reflection which are unwanted effects in typical lighting applications.

[0073] Therefore by using this fiber technology, as illustrated in figure 1 1 , a ring light 1 15 can be provided. A number of light engines 1 10a, 1 10b, 1 10c provide light via respective optical fibers or fiber bundles 1 1 1 a, 1 1 1 b, 1 1 1 c to central fiber cable 1 13. The fibers from bundles 1 1 1 a, 1 1 1 b, and 1 1 1 c are randomly combined to form mixed output fiber bundles 1 1 1 d, 1 1 1 e, 1 1 1 f. If the light engines 1 10a, 1 10b, 1 10c provide identical spectra, the random combination of fibers may be omitted.

[0074] At the end of the cable 1 13, the fiber bundles 1 1 1 d, 1 1 1 e, 1 1 1 f are respectively connected to evenly distributed light distributing elements 1 12a, 1 12b, and 1 12c of light ring 1 15. A light distributing element is an optical element that receives light from at least one optical fiber and emits it, preferably in a predefined direction. Light ring 1 15 may have a central optical piece 1 14, such as a lens. A light distributing element can also comprise a light guide to spread the light over a larger area of the ring.

[0075] For clarity, the example of figure 1 1 shows three light engines, three incoming and outgoing fiber bundles, and three light distributing elements. However, the number of light distributing elements does not have to be equal to the number of light engines - a single light engine can provide light to a plurality of fibers. Typically, more than three light distribution elements will be used in a ring light, in order to provide a uniform lighting. The lighting may be focussed on a central spot somewhere in front of the lens 1 14 by the light distributing elements 1 12a, 1 12b, 1 12c.

[0076] The ring light 1 15 can deliver the light to the object at defined angles eliminating shading and reflection problems, specifically available in medical applications with moisturized objects (from blood, organ fluids or other types of fluid). The same is true when using the same configuration in industrial inspection like food inspection where an evenly distributed light cone is required without shading and with an even distribution of wavelength power. [0077] I n an embodiment, the light engine 53 according the invention is used to light up a Digital Light Mirror Device (DM D) and can be used in photodynamic therapy to steer the beam in the right direction. For this the output of the light fiber bundles is collimated in such a way that the complete beam covers the DMD and each mirror can be addressed to steer the light beam. Synchronization between wavelength and DM D mirror part is possible.

[0078] The invention also provides a light engine which allows combination of light with the same wavelength as well as combining LEDs which are from the same colour but different colour bins (colour bins are manufacturing controlled peak LED wavelengths which are very close together (usually +-5nm per bin). For example, . 470 nm blue LEDs come in 4 bins, Bin 1 having its peak at 470-475, Bin 2 having its peak at 475-480, Bin 3 having its peak at 480-485 and Bin 4 having its peak at 485- 490) figure 10a .Current light engines cannot take advantages of combining multiple LEDs from different bins because of the limited steep slope of the dichroic mirrors, effectively making these additions very inefficient. The invention makes it possible to combine LEDS from different bins as well as the same and different wavelengths, to make a high power broad spectrum controlled light engine (figure 10b).

[0079] I n the foregoing description of the figures, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the scope of the invention as summarized in the attached claims.

[0080] I n particular, combinations of specific features of various aspects of the invention may be made. An aspect of the invention may be further advantageously enhanced by adding a feature that was described in relation to another aspect of the invention.

[0081] It is to be understood that the invention is limited by the annexed claims and its technical equivalents only. I n this document and in its claims, the verb "to comprise" and its conjugations are used in their non-limiting sense to mean that items following the word are included, without excluding items not specifically mentioned. In addition, reference to an element by the indefinite article "a" or "an" does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article "a" or "an" thus usually means "at least one".

Claims

1. Light engine (54, 54') for a medical device, comprising

- a plurality of light sources (41),

- a plurality of optical fiber bundles (51 , 52), wherein each of the plurality of light sources is butt-coupled or otherwise coupled to an optical fiber bundle (51 , 52), so that the optical fiber bundle receives only light from the light source to which it is coupled, wherein the light engine comprises a first group of one or more light sources emitting a first spectrum and a second group of one or more light sources emitting a second spectrum, said first spectrum being a visible light spectrum and said second spectrum being an excitation spectrum of a fluorescence agent.

2. Light engine (54, 54') according to claim 1 , wherein the light sources (41) comprise one or more lasers, more particularly laser diodes, wherein a laser or laser diode is provided with a lens (57) for shaping a laser beam before the beam enters the fiber bundle.

3. Light engine (54, 54') according to claim 2, wherein the lens (57) is configured to shape the laser beam in order to enlarge the Numerical Aperture.

4. Light engine (54, 54') according to any of the previous claims, comprising a filtering module (60) configured to reduce, preferably to exclude, the light from at least the first group of one or more light sources at fluorescence emission wavelengths of the fluorescence agent.

5. Light engine (54, 54') according to any of the previous claims, wherein the light sources of the first group comprise one or more light emitting diodes, LEDs and the light sources of the second group comprise one or more lasers.

6. Light engine (54, 54') according to any of the previous claims, wherein a light source of the first group (1 10a) is coupled to a first optical fiber bundle (1 1 1 a) and a light source of the second group (1 10b) is coupled to a second optical fiber bundle (1 1 1 b), and optical fibers from the first and the second optical fiber bundle (1 1 1 b) are combined to form a further optical fiber bundle (1 1 1 d) for providing mixed light from the first and the second group.

7. Light engine (54, 54') according to any of the previous claims, wherein the filtering module (60) is adapted for receiving light from a plurality of optical fiber bundles (65) and directing said light through a filtering device (63) so that, depending on the wavelength of the light, a part of the light is transmitted through to an at least one outgoing optical fiber bundle (66) and another part of the light is redirected to an absorbing surface (64).

8. Light engine (54, 54') according to any of the previous claims, further provided with a mixing module (70), said mixing module comprising an enclosure connected to a plurality of incoming optical fiber bundles (71) and at least one outgoing optical fiber bundle (72), said incoming and outgoing optical fiber bundles having terminal faces opposite each other.

9. Light engine (54, 54') according to claim 7, wherein the terminal face of the at least one outgoing optical fiber bundle (72) is provided with a diffusing layer (75).

10. Light engine (54, 54') according to any of the previous claims, further provided with a attenuation module (80), said attenuation module comprising an enclosure connected to at least one incoming optical fiber bundle (85) and at least one outgoing optical fiber bundle (86), said incoming and outgoing fiber bundles (85, 86) having terminal faces opposite each other, and means for adjusting the distance (w) between the terminal faces.

1 1 . Light engine (54, 54') according to claim 10, further comprising absorbing material (81 , 82) surrounding the at least one incoming optical fiber bundle (85).

12. Light engine (54, 54') according to any of the previous claims, comprising

- an active cooling component, such as a Peltier element, for cooling at least one of the light sources; and

- control electronics for measuring and controlling the temperature of the at least one light source in order to minimize wavelength shift of the light source light.

13. Light engine (54, 54') according to claim 12, wherein the output light power is controllable and stable for allowing quantitative measurements in fluorescent image guided surgery.

14. System of a light engine (54, 54') according to any of the previous claims and a camera, wherein the light engine is adapted to control the emitted light in

dependence of the camera exposure time.

15. System of claim 14, comprising a controller which is programmed with a light source sequence program that is connected to the camera for control of the light in relation to the camera exposure time.

16. System of claim 15, wherein the camera is configured to monitor the

fluorescence radiation on a first detection channel and the excitation radiation on a second channel, and wherein the controller is configured to control the light sources of the light engine in dependence of both signals.

17. System of a light engine (54, 54') according to any of the previous claims 1 -13 and a ring light (1 15) adapted to receive light from the light engine via at least one optical fiber bundle, wherein the light ring comprises a ring with light distributing elements (1 12a, 1 12b, 1 12c), wherein each light distributing element is connected to at least one optical fiber from the at least one optical fiber bundle.

18. System according to claim 17, wherein a plurality of light engines (54, 1 10a, 1 10b, 1 10c) are connected to an optical fiber cable (1 13) comprising a plurality of optical fiber bundles (1 1 1 a, 1 1 1 b, 1 1 1 c), each light engine providing light to at least one optical fiber bundle.

19. System according to claim 17 or 18, further comprising an imaging system for fluorescence imaging, wherein the light engine is adapted to provide light

- comprising light at a visible wavelength;

- comprising light at an excitation wavelength of a fluorescence agent, and

- not comprising light at a fluorescence wavelength of the fluorescence agent, wherein the imaging system is adapted to detect reflected light at the visible wavelength and light at a fluorescence wavelength coming from the fluorescence agent.

20. System of a light engine (54, 54') according to any of the previous claims 1 -13 and a laparoscope (90).