The object of the invention relates to a multi-channel illuminator for the production of an electromagnetic output beam, especially for fluorescence microscopes, which illuminator has an optical main axis, and which illuminator having at least two light sources that each have an optical axis and capable of emitting an electromagnetic beam along the optical axes.

Fluorescence microscopes use high-luminescence light sources that are suitably intense in the blue and UV range. Due to this mercury and xenon arc lamps are conventionally used to a wide extent instead of normal incandescent lamps. High luminescence is required due to the special demands of microscopy, where one square millimetre or even smaller areas need to be typically illuminated.

The most widespread light source in fluorescence microscopy is the mercury vapour lamp, the emission spectrum of which is not continuous; instead it has well-defined emission peaks. This is the reason why the manufacturers of fluorescent dyes have developed dyes that may be optimally excited at these peaks. Currently, these dyes are the most commonly used in microscopy. The disadvantage of mercury vapour lamps is that they are not very efficient. The light output of a 100 W mercury vapour lamp is approximately 4 W, in other words about 300 mW per peak.

During the past decade the luminous intensity of LEDs has risen to such a degree that the use of LEDs in fluorescence microscopy has become a realistic possibility. The advantage of LEDs is that their efficiency is much greater than that of mercury vapour lamps. In the case of microscope lamps that use LEDs, the electromagnetic radiation corresponding to the emission peaks of the mercury vapour lamp is generated with LEDs illuminating in different channels, at various wavelengths. In fluorescence microscopy most frequently 3 difference fluorescent dyes are used at the same time in a sample, but even more may be used in certain research applications. The 3 dyes that are used may also vary according to the sample, therefore in the case of the currently known solutions lamps with 4 to 16 channels are generally used. In the case of these microscope lamps the light beams of the individual channels are combined and guided out of the lamp with the use of dichroic filters (also known as dichroic mirrors). An example of a microscope lamp operating on the basis of this principle is presented in US patent number US 8,203,784.

The disadvantage of the above system is that the use of dichroic filters is expensive (currently costing several hundreds of dollars each); furthermore the transmittance of dichroic filters is not 100%, not even at the designed wavelength. This value, even in the case of the best filters currently available, is only around 95%. If the beam created in the given channel has to pass through several dichroic filters, then the intensity of the light will drop considerably. Using the above example, assuming four filters, even according to an optimistic estimate 20% of the light will be lost.

A further disadvantage of the multi-channel microscope lamps currently existing is that they are not capable of producing certain wavelength beams. The reason for this is that dichroic filters in practice do not have a Dirac-delta rising edge, in other words the change between the transmitted and reflected wavelength ranges is not sharp. As a consequence, the light falling here is lost. The width of the edge rising from a transmission value of 10% to 90% is typically 10 or more nm. In the case of several filters positioned one after the other these wavelength ranges are combined, which represents a significant covering of the spectrum. The steepness of rising edges is reduced by manufacturers by vapour coating several layers onto the filter, which increases the price even more. Over the past decades the rising edge of dichroic filters has not really dropped under 10 nm, and it is not expected that this situation will significantly improve in the near future.

A further problem of multi-channel systems using LEDs is that sufficiently strong LEDs can only be manufactured in the blue and red wavelength ranges, but not in the green range. Therefore the electromagnetic beam needs to be produced in another way in the wavelength range between 500-600 nm. In the field of microscope lamps this problem was first solved by a company called Lumencor by exciting a fluorescent rod from the side using LEDs. The rod acts as a light guide, and the light excited by the LEDs exits the end of the rod combined. For example, the X-Cite Fire type microscope lamp made by the Excelitas company works on this principle. The greatest disadvantage of this solution is that it is large and costly. In the case of the aforementioned solution 80 LEDs are used to excite the rod. The output of the drive electronics, the cooling and space required for the system are proportionate with this number. Another problem is that due to the large number of LEDs, cooling can only be carried out actively, using fans. The vibrations created by motors usually cause a problem in microscopy. It is the fans that cause the greatest problem, because the vibrations generated constantly during the exposure time of several hundreds of milliseconds reduce the image quality. A partial solution to this problem is presented by liquid Light Guide (LLG) lamps, however, from the point of view of the use of the light, this is not the best solution. A fluorescent lamp needs to be good approximately in the 365 to 750 nm range. However, none of the currently known light guides meets this condition particularly well, because even at the best wavelengths 20% of the light is lost. Another problem of the light guides is that their diameter is 3 to 5 mm, therefore an overly large surface produces light at their ends, which light cannot be optimally collected into the microscope.

According to another method the light output of the LEDs emitted in the green wavelength range is increased by applying a phosphor layer to the LEDs, which converts the blue light of the LED to longer wavelengths. Here the phosphor is not a chemical element, instead it is a substance similar to the phosphor used in cathode ray tubes. The disadvantage of this solution is that only a relatively low output can be achieved in this way. The conversion factor of the phosphor is good, around 90%. The problem is derived from the fact that the excited phosphorous crystals emit light in all directions, therefore half of the light is radiated back towards the LED. Also, the light output of LEDs drops as temperature increases, and the dissipation of the heat sets a limit to the luminance of the LEDs. The other problem is that the LED illuminates the phosphor from below. If the layer is too thin then the large proportion of the blue light is transmitted and not converted. Also, if it is too thick, then the light of the bottommost phosphor layer also has to pass through the layer above it, which reduces efficiency. It was recognised that by suitably arranging light sources radiating at various wavelengths and a rotating mirror, a multi-channel illuminator may be created without the use of dichroic filters and fan cooling, in addition the external excitation of the light sources may be implemented simply and efficiently.

The objective of the present invention is to provide a multi-channel illuminator that is free of the disadvantages of the solutions according to the state of the art, especially the provision of a multi-channel microscope lamp with which output beams of various wavelength can be produced without any significant loss of light.

The objective of the invention is also the provision of a multi-channel illuminator, especially of a multi-channel microscope lamp that contains one or more light sources that are excited from outside, and which can be excited simply and efficiently.

A further objective of the present invention is to provide a multi-channel illuminator, in particular a multi-channel microscope lamp that does not need active fan cooling, so that it can be fitted to the microscope directly without deteriorating the microscope’s imaging.

According to the invention, these objectives are achieved by a multi channel illuminator according to claim 1.

Some preferred embodiments of the invention are defined in the dependent claims.

Further details of the invention will be explained by way of exemplary embodiments with reference to the figures, wherein

Figure 1 shows a schematic cross-sectional view of a preferred embodiment of the multi-channel illuminator according to the invention without the excitation light source,

Figure 2a shows a schematic side cross-sectional view of the embodiment of the multi-channel illuminator according to the invention shown in figure 1 together with the excitation light source, with the dichroic mirror in its first position,

Figure 2b shows a schematic side cross-sectional view of the embodiment of the multi-channel illuminator according to the invention shown in figure 2a with the dichroic mirror tilted out of its first position,

Figure 3 illustrates a schematic perspective view of the embodiment of the multi-channel illuminator according to the invention shown in figure 1 ,

Figure 4 illustrates a schematic cross-sectional view of a modular embodiment of the light source according to the invention.

Figure 1 shows a schematic cross-sectional view of a multi-channel illuminator 10 according to the invention. The illuminator 10 serves for producing an electromagnetic output beam 100, which may be especially used for illuminating the slides of fluorescence microscopes. In the context of the present invention the concept of beam is understood to mean any parallel, focussed or diverging electromagnetic beam in the visible light or near visible light (e.g. infrared or UV) wavelength range, the cross-section of which is preferably circular, but it may also be square or even rectangular as well. The illuminator 10 has an optical main axis 12 parallel to the direction of propagation of the output beam 100. In other words, the optical main axis 12 substantially coincides with the axis of symmetry of the output beam 100.

The illuminator 10 according to the invention contains a frame structure 1 1 made from preferably metal (such as aluminium) or other material providing suitable structural stability (e.g. plastic composite), which serves for securing the components of the illuminator 10. The illuminator 10 contains at least two light sources 16 fixed to the frame structure 11 and having an optical axis 14 for emitting an electromagnetic beam 101 along the optical axis 14. The beam 101 has a wavelength range, i.e. spectra intensity distribution characteristic of the emitting light source 16. It should be noted that the wavelength ranges of the beams 101 emitted by the individual light sources 16 are different (in other words they cover different parts of the spectrum), but optionally they may even partially overlap each other. The light source 16 preferably contains an LED 16a for emitting an electromagnetic beam 101 , or a photo-luminescent substance 16b that can be excited by an electromagnetic exciting beam, as is known by a person skilled in the art. It should be noted that in the context of the present specification phosphor is understood to mean the so-called light powder known to persons skilled in the art, and not the chemical element in the periodic table, which does not necessarily contain phosphorous atoms. The phosphors used in the light source 16 may be, for example, transition or rare earth metal compounds, such as oxides, silicates, sulphides or halides. The beam 101 emitted from the light source 16, similarly to the output beam 100, may be parallel, focussed or diverging. The optical axis 14 is understood to mean the axis pointing in the direction of propagation of the beam 101 leaving the light source 16, which substantially coincides with the axis of symmetry of the beam 101. Optionally the light source 16 contains one or more optical elements 200, such as lenses and/or auxiliary mirrors for focussing or diverging the beam 101. In this case the optical axis 14 is obviously understood to mean the axis pointing in the direction of propagation of the beam 101 exiting or reflected from the optical element 200.

In the case of a preferred embodiment the light sources 16 are arranged in modules 18 connected to the illuminator 10 in a releasable way, such as with a screw thread, preferably supplied with a thermometer sensor 18a and/or a light meter sensor 18b and/or a control unit 18c for operating the LED 16a of the light source 16 as shown, for example, in figure 3. The thermometer sensor 18a and the light meter sensor 18b are designed to determine the temperature or light output of the LED 16a of the light source 16 (or, optionally, the excited photo- luminescent substance 16b). As it is known, the light output of LEDs depends on temperature. Therefore, in the case of an especially preferred embodiment, in order to avoid transient phenomena, the control unit 18c is provided as an EEPROM 18c’ in data connection with the temperature sensor 18a adapted for storing the temperature-dependent characteristics of the LED 16a of the light source 16, and adapted for regulating the electric current used by the LED 16a as a function of the stored characteristics to ensure constant luminance. By means of the EEPROM 18c’ the current used by the LED 16a of the light source may be continuously regulated in accordance with the temperature of the LED 16a, so that the luminous intensity generated by the LED 16a can be maintained at a substantially constant value practically from the moment of switching on. It should be noted that optionally embodiments are conceivable in the case of which the illuminator 10 has a single light meter sensor 18b, preferably arranged in the proximity of the optical main axis 12, and a single control unit 18c, which light meter sensor 18b and control unit 18c are provided not in the modules 18, but, instead, in the frame structure 1 1 , for example. The advantage of this is that it is not necessary to provide all of the modules 18 with a separate light meter sensor 18b and control unit 18c. The light meter sensor 18b may be arranged, for example, along the optical main axis 12, so as to measure the light intensity of the beam 101 emitted by any light source 16. The control unit 18c is in a control connection with all LED 16a, and stores the temperature-dependent characteristic of all LEDs 16a.

In the case of a preferred embodiment the module 18 contains a heat dissipation unit 20, preferably passive cooling ribs 20’ arranged outside of the illuminator 10 for removing the heat energy generated in the course of the emitting of the electromagnetic beam 101 , by the LED 16a or the excitement beam, from the light source 16, as it can be seen in figures 3 or 4. The cooling ribs 20’ is a heat dissipation device made from a material with good heat transmittance (e.g. aluminium, copper, a composite containing metal, etc.) with a large heat dissipation surface contacting with the light source 16 and with the air surrounding the illuminator 10, as is obvious for a person skilled in the art. The heat exchanger unit 20 is preferably dimensioned to provide for cooling of the light source 16 without the use of moving elements (e.g., fans). It should be noted that optionally embodiments are conceivable in the case of which the heat dissipation unit 20 contains an electric cooling device, such as a Peltier element.

In the case of the embodiment shown in figure 4 the photo-luminescent substance 16b is pressed onto the heat dissipation unit 20 in a thin layer with a transparent securing device 22 preferably formed as a glass sheet or glass lens. In other words the photo-luminescent substance 16b is not separately embedded into any material, the photo-luminescent material 16b is secured to the heat dissipation unit 20 by the pressure exerted by the securing device 22. The excitement of the photo-luminescent substance 16b takes place through the securing device 22 in such a way that the exciting electromagnetic beam illuminates the photo- luminescent substance 16b by passing through the securing device 22, which gets into excited state due to the effect of this. By returning from excited state to ground state the photo-luminescent substance 16b emits light, which passes through the securing device 22 to exit the light source 16.

The light sources 16 are arranged in the illuminator 10 according to the invention in such a way that the optical axes 14 of the light sources intersect one another at the first intersection point M1 located on the optical main axis 12, and the individual optical axes 14 are at the same angle to the optical main axis 12. In the case of the preferred embodiment shown in figures 2a and 2b the light sources 16 are in a plane passing through the first intersection point M1 and perpendicular to the optical main axis 12, and arranged along a circular arc that has the first intersection point M1 as its centre, therefore the optical axes 14 are at the same right angle to the optical main axis 12. Naturally, optionally embodiments may be conceived in the case of which the light sources 16 are arranged in a plane passing through the first intersection point M1 , and perpendicular to the optical main axis 12, but not along a circular arc.

In the case of another exemplary embodiment the light sources 16 are arranged so that the optical axes 14 are located on the mantle of a cone with its vertex at the first intersection point M1 and with axis of symmetry that coincides with the optical main axis 12 (not illustrated).

In the case of the illuminator 10 according to the invention, a mirror 30 is arranged at the first intersection point M1 rotatably around the optical main axis 12 into positions corresponding to the individual optical axes 14, in such a way that in each position corresponding to an optical axis 14 the normal vector N1 of the reflective surface 31 of the mirror 30 passing through the first intersection point M1 coincides with the angle bisector of the angle between the optical main axis 12 and the given optical axis 14. Mirror 30 is understood to mean an optical element well known to a person skilled in the art that reflects the beam 101 created by the light source 16 and arriving at the reflective surface 31 in accordance with the laws of light reflection. In other words, by rotating into a position corresponding to a given optical axis 14, the mirror 30 reflects the beam 101 , arriving from the given optical axis 14 and striking the reflective surface 31 , along the optical main axis 12. It should be noted that in the context of the present specification the beam 101 reflected from the reflective surface 31 is called an output beam 100.

The mirror 30 is preferably formed as a plane mirror, but optionally the mirror 30 can also be a mirror with a concave reflective surface 31 , for example, which reflects an incoming diverging beam 101 to make it parallel. In the case of the embodiment shown in figures 2a and 2b the mirror 30 is a plane mirror that is at a 45-degree angle to the optical main axis 12, and the normal vector N1 of which passing through the first intersection point M1 , in other words its surface normal is also at a 45-degree angle to the optical main axis 12. In the context of the present invention the positions corresponding to the individual optical axes 14 is understood to mean those positions in the case of which the normal vector N1 of the mirror 30 is in the plane determined by the given optical axis 14 and the optical main axis 12, and on the angle bisector of the given optical axis 14 and the optical main axis 12. By rotating the mirror 30 the normal vector N1 passing through the first intersection point M1 rotates around the mantle of a cone with its vertex at the first intersection point M1 , axis of symmetry coinciding with the optical main axis 12, and with a cone angle equal to the angle between the normal vector N1 and the optical main axis 12.

In the case of a preferred embodiment the rotation of the mirror 30 around the optical main axis 12 into the positions corresponding to the individual optical axes 14 is provided by an electric motor 32 connected to the mirror 30 and having an axle coinciding with the optical main axis 12. In the case of this embodiment the mirror 30 is connected directly to the axle of the motor 32 at the first intersection point M1. The electric motor 32 may be provided, for example, as a stepper motor well known to a person skilled in the art, with the help of which the mirror 30 can be rotated around the optical main axis 12 by the desired angle preferably in a few ms from one position to another.

In a particularly preferred embodiment, the lighting device 10 comprises an excitation light source 34 having an excitation optical axis 15 for emitting an electromagnetic excitation beam 102 along the excitation optical axis 15. The excitation beam 102 serves to excite the photo-luminescent substance 16b of the light source 16. The wavelength of the excitation beam 102 is substantially between a first wavelength value and a second wavelength value smaller than the first wavelength value, in other words the spectral intensity of the excitation beam 102 is distributed among the wavelengths between the first and second wavelength values.

In the context of the present specification excitation optical axis means the axis pointing in (lying along the path of) the direction of propagation of the excitation beam 102 leaving the excitation light source 34, which substantially coincides with the axis of symmetry of the excitation beam 102. The cross-section of the excitation beam 102 may be, for example, circular, ellipsoid, square or rectangular in shape. In the case of a preferred embodiment the excitation light source 34 contains at least one laser, preferably a diode laser (not shown in the figures) adapted for emitting the electromagnetic excitation beam 102.

Great light intensity may be achieved with diode lasers in a cost-efficient way. However, it was recognised that the cross-section of the beam created by diode lasers is not a regular circle or square, but a Gauss distribution line, with which the excitation of the photo-luminescent substance 16b is not efficient. Precisely because of this, in the case of an especially preferred embodiment, the excitation light source 34 contains two or more lasers, and optical fibres 36 for combining the excitation beams 102 emitted by the lasers, adapted for transmitting and emitting the combined beams, such as optical fibres 36 that have circular or square shaped input and output openings, preferably multimodal optical fibres known of to a person skilled in the art. In the case of this embodiment the light of the lasers is introduced into the input opening of the optical fibre 36. As a result of the many reflections in the optical fibre 36 the light of the lasers becomes mixed up and exits the regularly shaped output opening with combined intensity. In this case the excitation optical axis 15 is understood to mean the axis pointing in the direction of propagation of the excitation beam exiting the outlet opening of the optical fibre 36 (lying along the direction of propagation).

In the case of the illuminator 10 according to the invention the excitation light source 34 is arranged so that the excitation optical axis 15 intersects the optical main axis 12 at a second intersection point M2 located at a distance from the first intersection point M1 in the direction of propagation of the output beam 100, as shown in figures 2a and 2b. An input opening 13 is formed on the frame structure 11 and the excitation light source 34 is connected to the input opening 13. In the case of a preferred embodiment the excitation light source 34 is connected to the frame structure 1 1 in a releasable way, in this way it may even be removed if required. In this case the input opening 13 may be closed with a suitably designed means (e.g. with a stopper).

A dichroic mirror 40 that substantially reflects the excitation beam 102 and that substantially transmits electromagnetic radiation of a wavelength greater than the first wavelength value is arranged in the second intersection point M2 in a first position so that the normal vector N2 of the surface of the dichroic mirror 40 facing the excitation light source 34 passing through the second intersection point M2 coincides with the angle bisector of the angle between the optical main axis 12 and the excitation optical axis 15 (see figure 2a). In other words in the first position the dichroic mirror 40 reflects the excitation beam 102 arriving at its surface from the direction of the excitation optical axis 15 along the optical main axis 12, in the direction of the mirror 30. The optical main axis 12, and the output beam 100 starting from the reflective surface 31 of the mirror 30 pass through the dichroic mirror 40 arranged in the first position. It should be noted that the expressions “substantially reflecting” and “substantially transmitting” are used because in practice there is no dichroic mirror 40 (dichroic filter) that completely (100%) transmits or reflects the light incident on it. The transmission (or reflection) efficiency of the best dichroic mirrors 40 currently commercially available is around 95% at the most.

In the case of an especially preferred embodiment the illuminator 10 contains a drive means 42 for removing the dichroic mirror 40 from the second intersection point M2 and the optical main axis 12 and for returning it to the first position, preferably an electric drive means 42. In the case of the preferred embodiment depicted in figures 1 to 3 the drive means 42 contains an electric stepper motor 42’ connected to the end of the dichroic mirror 40. By operating the stepper motor 42’ of the drive means 42 the dichroic mirror 40 may be moved (tilted) out of the first position. In the tilted position of the dichroic mirror 40 the optical main axis 12 and the output beam 100 will not cross the dichroic mirror 40 (see figure 2b). It should be noted that other embodiments may be conceived wherein the removal of the dichroic mirror 40 from the first position is done manually by the user, not by means of the drive means 42.

In the case of another possible embodiment the wavelength of the excitation beam 102 falls between the first wavelength value and a second wavelength value smaller than the first wavelength value, and the dichroic mirror 40 allowing the excitation beam 102 to be substantially reflected and allowing electromagnetic radiation of a wavelength greater than the first wavelength value and smaller than the second wavelength value to be substantially transmitted. In other words, the dichroic mirror 40 only reflects electromagnetic radiation in the wavelength range of the excitation beam 102, and transmits radiation with a wavelength greater or smaller than this. As the wavelength range of the excitation beam 102 is usually narrow in practice, the dichroic mirror 40 is only able to deflect the output beam 100 in a narrow range at the most, therefore causing only a slight degree of reduction in light intensity. In the case of this embodiment it is not absolutely necessary to use the drive means 42, and the dichroic mirror 40 may even be installed in the first position in a fixed way, in this way the illuminator 10 is simpler and cheaper to produce.

The operation of the illuminator 10 according to the invention is presented in the following with reference to the individual figures.

The multi-channel illuminator 10 according to the invention used to produce output beams 100 in various wavelength ranges, the area of application of which is especially fluorescence microscopy. The embodiment of the illuminator 10 shown in figure 3 contains eight light sources 16 arranged in modules 18, in other words it contains eight channels. Some of the light sources 16 contain a LED 16a, and others contain a photo-luminescent substance 16b. The various light sources 16 can produce beams 101 in various wavelength ranges with which various fluorescent dyes can be excited.

After the light source 16 to be used has been selected, the mirror is rotated to the position belonging to the optical axis 14 of the selected light source 16. If the light source 16 to be used contains a LED 16a, then the dichroic mirror 40 is preferably removed from the light path defined by the optical main axis 12 (see figure 2b), so it does not reduce the intensity of the output beam 100. The light source 16 is switched on after the mirror 30 has been rotated to the desired position. The beam 101 produced by the light source 16 strikes the reflective surface 31 of the mirror 30, from where it is reflected into the direction of the optical main axis 12 and leaves the illuminator 10 as output beam 100. It should be noted that conventionally used optical elements, such as one or more lenses 46, may be optionally placed in the path of the output beam 100, as shown in figure 1. If another light source 16 containing an LED 16a is to be used, the mirror 30 must be rotated to the position belonging to the optical axis 14 of the selected new light source 16. In this way switching between the various light sources 16 can be carried out quickly (in a few ms) and simply, without the use of various filters. If a light source 16 is to be used that contains photo-luminescent substance 16b, the dichroic mirror 40, if moveable, is moved to first position, and the mirror 30 is moved to the position belonging to the optical axis 14 of the selected light source 16. Subsequently, an excitation beam 102 is produced with the excitation light source 34, which strikes the surface of the dichroic mirror 40 along the excitation optical axis 15, then it is reflected from there along the optical main axis 12 towards the mirror 30. The mirror 30 reflects the excitation beam 102 arriving from the direction of the optical main axis 12 to the photo-luminescent substance 16b of the selected light source 16, which enters into excited state due to the effect of the excitation beam 102. When the photo-luminescent substance 16b returns to the ground state it radiates a beam 101 with a wavelength longer than the first wavelength value of the excitation beam 102, which is radiated along the optical axis 14 of the light source 16 to the reflective surface 31 of the mirror 30, from where it is reflected as output beam 100 in the direction of the optical main axis 12 through the dichroic mirror 40 in first position to then exit the illuminator 10. The dichroic mirror 40 is configured to substantially reflect the excitation beam 102, and substantially transmit the beam 101 with a greater wavelength than the first wavelength value. Thus, the photo-luminescent substance 16b of the light source 16 can be continuously excited by the excitation beam 102.

The advantage of the multi-channel illuminator 10 according to the invention is that the beams 101 generated by the various light sources 16 are not guided out with a filter system, in this way avoiding any significant drop in light intensity. Another advantage of the illuminator 10 is that its rotating mirror design makes it possible to use not only LED but also excited light sources, and as a result of its modular construction the light sources can be easily replaced as required, even by the user. Yet another important advantage is that the photo- luminescent substances 16b of the light sources 16 can be excited separately, yet with a single excitation light source 34, without increasing size or the costs. Also, where there is no need for excitation beams, the excitation light source 34 and the light sources 16 containing photo-luminescent substance 16b can even be omitted. Due to the arrangement of the light sources, the lighting device 10 does not require active fan cooling, so it can be connected directly to the microscope, even without a light guide, thus avoiding the significant loss of light.

Various modifications to the above disclosed embodiments will be apparent to a person skilled in the art without departing from the scope of protection determined by the attached claims.