Patent ID: 12189109

DETAILED DESCRIPTION

In cooperation with attached drawings, the technical contents and detailed description of the present inventive concept are described thereinafter according to a preferable embodiment, being not used to limit the claimed scope. This inventive concept may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the inventive concept to the skilled person.

FIG.1illustrates a light distribution device100according to an embodiment. The light distribution device100comprises six waveguides110. Each waveguide110is made of a transparent optical material. Each waveguide110is configured for propagation of light along an extension of the waveguide110. Light from a light source (not shown) may be received at an entrance114of each waveguide110and propagated from the entrance114along the extension of the waveguide. Each waveguide comprises a light coupling portion112.

The light distribution device100further comprises a slab layer120. The slab layer120is a planar structure extending in a plane in two directions. InFIG.1the slab layer120is illustrated as having a rectangular shape in the plane, however it should be understood that the slab layer120may have different shapes as well, other than being rectangular. In the direction perpendicular to the plane, the slab layer120has a limited extension. The extension in the direction perpendicular to the plane may be equal or similar to the extension of the waveguide110in the same direction. The slab layer120is made of a transparent optical material, and is configured for propagation of light in the plane.

At a boundary125of the slab layer120in the plane, the slab layer120comprises light coupling edges122. The waveguides110are arranged in the plane around the boundary125such that the light coupling portions112of the waveguides110extend alongside and at a distance from one of the light coupling edges122of the slab layer120. By the present arrangement a gap130is formed between the light coupling portions112and the light coupling edges122.

The waveguides110and the slab layer120are arranged and configured to allow at least some of the light being propagated in the waveguides110to be coupled into the slab layer120from each of the light coupling portions112through the corresponding light coupling edges122across the gap130. In other words, at least part of the light beam propagating in each waveguide110may leak across the gap130into the slab layer120.

The slab layer120is configured to propagate the light coupled into the slab layer120from each of the waveguides110. The light from each of the waveguides is directed towards an interference region126of the slab layer120such that an interference pattern is formed by interference of light in the interference region126.

In the light distribution device100, the waveguides110are arranged with respect to the slab layer120such that three opposing light beam pairs are formed. Each pair comprises a first waveguide110aand a second waveguide110b. The light coupling portion112aof the first waveguide110aextends alongside a first light coupling edge122aof the slab layer120. Further, the light coupling portion112bof the second waveguide110bextends alongside a second light coupling edge122bof the slab layer. By the present arrangement an interference pattern may be formed by interference of light being coupled into the slab layer120from at least the first waveguide110ato the first light coupling edge122a, and the second waveguide110bto the second light coupling edge122b.

The interference pattern formed when light is coupled into only one such pair, may consist of equidistant bright and dark interference fringes, as shown in i), ii), and iii) respectively, inFIG.1. By activating two or more pairs of waveguides110, more complex interference patterns may be generated.

It should be understood that forming opposing light beam pairs in the slab layer120is not strictly necessary by the inventive concept, but also other alternatives are possible. By way of example, an interference pattern may be formed by interference between the light coupled from a single waveguide110into the slab layer120and its reflection, or between the light coupled from two waveguides110not forming an opposing pair. More details on how the interference may be achieved are given in relation to some of the following figures.

It is realized that by altering a property of the light waves or the medium in which the light waves propagate, the interference pattern may be altered. This is an advantage for example when the light distribution device100is used as illumination in an imaging system for imaging a sample arranged in close relation to the slab layer120, such as on top of the slab layer120. The light distribution device100is a compact device for generating structured illumination for illuminating different portions of the sample. By altering a property of the light wave or of the medium, the structured illumination may be changed into different patterns illuminating different portions of the sample, and in this manner build up a high-resolution image of the full sample. The present arrangement allows control of the interference pattern by tuning a phase, a wavelength, an amplitude, or a polarization of light propagated in the waveguides110. Such tuning may be realized by arranging an influencing device such as a phase shifter, a wavelength shifter etc., in the path of the light from the light source, prior to the entrance114of the individual waveguides110. Such influencing devices may either be part of the light distribution device100or be separate parts connectable to the light distribution device100. Alternatively and/or additionally, control of the interference pattern may be achieved by tuning a medium property of the slab layer120and/or the waveguides110. In case the arrangement comprises a plurality of waveguides110as shown inFIG.1, control of the interference pattern may be achieved by control of active waveguides110. Such control may be in the form of switches opening and closing the individual entrances114of the waveguides110. More details on control of the interference are given in relation to some of the following figures.

FIG.2Aschematically illustrates further details related to the light coupling from one of the waveguides110to a slab layer120, in the light distribution device100. Light from a light source (not shown) may be received at the entrance114of the waveguide110. The light propagation direction in the light coupling portion112coincides with a direction in which the light coupling portion112is elongated, namely along the x-axis. In this manner the light propagating direction extends alongside the light coupling edge122of the slab layer120.

The slab layer120is arranged alongside the light coupling portion112. More specifically, the light coupling portion112of the waveguide120extends in parallel with the light coupling edge122of the slab layer120. However, it should be understood that other alternatives to the light coupling portion112being parallel with the light coupling edge122are possible. For example, the light coupling portion112may be inclined with respect to the light coupling edge122. Alternatively, the light coupling portion112may have a curved shape such that not all parts of the light coupling portion112can be simultaneously parallel with the light coupling edge122. By way of example, the light coupling portion112and thus the gap130profile may have a periodically varying shape, such as a sinusoidal shape.

The light coupling portion112of the waveguide110extends alongside and at a distance from the light coupling edge122of the slab layer120forming the gap130between the light coupling portion112and the light coupling edge122. The coupling of light across the gap130may occur continuously along a significant portion of the light coupling portion112and the corresponding light coupling edge122.

By the present arrangement, a light beam with a collimated, coherent wavefront is propagated in the slab layer120with an angle θ with respect to the light coupling edge122. The angle θ is dependent on the width w of the waveguide110such that as the width w of the waveguide110gets larger, the angle θ between the light coupling edge122and the light propagation direction Din the slab layer120becomes smaller.

The dependence of the angle θ on the width w of the waveguide110may follow the behavior illustrated in the graph ofFIG.2B. Thus, by tuning the width w of the waveguide110, the angle θ can be altered and thereby a desired direction D of propagation can be obtained. In this manner it may be ensured that the light beam is propagated to a desired interference region of the slab layer120.

As illustrated inFIG.2Athe slab layer120may be arranged with respect to the waveguide110to propagate the light coupled into the slab layer120from the waveguide110such that the width of the cross-section of the light in the slab layer120, is larger than the width of the cross-section of the light in the waveguide110. Expressed differently, the narrow light beam of the waveguide110may be expanded within the plane of the slab layer120when coupled into the slab layer120. The level of beam expansion is dependent on the distance between the light coupling portion112and the light coupling edge122, i.e. the gap130. Hence, by tuning the gap130the width expansion of the light beam in the slab layer120may be altered. It should be understood that although the beam is illustrated inFIG.2Aas being expanded when being coupled from the waveguide110into the slab layer120, expansion is not necessary and so the width of the light beam in the slab layer120may be the same as the width of the beam in the waveguide110.

The possibility of selecting a certain direction of propagation and a width of the light beam in the slab layer120, in combination with the properties of the collimated, coherent wavefront, may contribute to a stable and controllable interference pattern.

FIG.2Cillustrates a graph showing how the gap between the light coupling portion and the light coupling edge may vary along the extension of the light coupling portion. Although the gap130inFIG.2Ais illustrated as being the same along the extension of the light coupling portion, the gap may alternatively be different at different positions. Thus, the distance between the light coupling portion and the light coupling edge in the gap is different at different positions along the light coupling portion, such that a gap profile between the light coupling portion and the light coupling edge is non-uniform.

Due to phase matching property between the waveguide and the slab layer, a profile shape set by the power distribution in the waveguide is transferred to the slab layer. A general gap profile g(x) may be expressed as:

g⁡(x)=-1b⁢log⁢(1a⁢f⁡(x)1-∫-∞xf⁡(ξ)⁢d⁢ξ)

where x denotes a position along the extension of the light coupling portion.

The coefficients a and b may be chosen based on numerical mode analysis of the waveguide and will tune the desired slab mode. The coefficients a and b may be found from the exponential power leakage between the waveguide and the slab layer, relating them to the imaginary part of the effective refractive index, neff, by the following expression:
Im(neff)=a·exp(−b·g(x))

The profile function f(x) of the power density in the slab layer is chosen depending on the application criteria. A super-gaussian profile having a near-constant intensity profile over a large region is a preferable power density profile when generating interference patterns in structured illumination microscopy. The profile function may be expressed as:

f⁡(x)=A·exp⁡(-(x22·w2)n)

where A is a normalization constant, w is the width of the waveguide and n is the power of the super-gaussian profile.

FIG.3A-Bschematically illustrates an advantage with using the coupling of light from a waveguide into a slab layer as a beam expander, compared to conventional adiabatic taper beam expansion.FIG.3Aillustrates that, by means of the light distribution device100the width w of the light beam in the waveguide110may be expanded to a width W of the light beam in the slab layer120. The length required to achieve this beam expansion is here denoted L1. By way of example, the width w of the light beam in the waveguide110may be in the range of 0.2-1.2 μm prior to expansion. By way of further example, the width W of the light beam in the slab layer120may be in the range of 30-10 000 μm, after expansion. Thus, the light distribution device100may easily provide a width expansion of ˜25 times or more, with substantially maintained beam quality.

FIG.3Billustrates beam expansion by conventional adiabatic taper, from a beam width w in a waveguide10to a beam width Win a slab layer20. The adiabatic taper relies on linearly expanding the light beam and thus to achieve the same level of beam expansion by means of conventional adiabatic taper as with the light distribution device100, the distance between a waveguide10and a slab layer20, were denoted L2, is significantly longer than L1. An adiabatic taper may have a length in order provide a width expansion of up to ˜20 times. However, providing larger width expansions in order to generate very wide beams of more than 100 μm with adiabatic tapers is very challenging without losing beam quality. The light distribution device, on the other hand, does maintain a good beam quality for large widths. Further, such beam expansions may be achieved with minimal additional component space of say 1:100 compared to conventional adiabatic taper. Also, beam expansion may be provided along a light coupling edge of the slab layer, wherein the edge is anyway needed in the slab layer such that length of the light coupling portion of the waveguide does not add to the footprint of the light distribution device100. By means of the light distribution device100as part of the illumination of an imaging system, a compact illumination system yet with a large field-of-view may be provided.

FIG.4illustrates a light distribution device200according to another embodiment comprising a triangularly shaped slab layer220. The slab layer220is arranged onto a top surface of a substrate240. At the boundary225of the slab layer220, the slab layer220comprises light coupling edges222. Six waveguides210are arranged on the substrate240around the boundary225such that the light coupling portions212of the waveguides210extend alongside and at a distance from one of the light coupling edges222. By the present arrangement a gap230is formed between the light coupling portions212and the light coupling edges222.

Each waveguide210may further comprise an input portion216extending in the plane in a direction towards the corresponding light coupling edge222of the slab layer220. The input portion216comprises an entrance214at which light from a light source may be received. The input portion216is optically connected at an angle to an input end213of the light coupling portion212.

Through the entrance214the input portion216may receive light. The received light may be directed along the input portion216to the input end213of the light coupling portion212such that light in the input portion216propagates towards the light coupling edge222of the slab layer220. Upon reaching the input end213of the light coupling portion212light is redirected to propagate in the light coupling portion212alongside the light coupling edge222of the slab layer120.

Similarly as to what was described in relation toFIG.1andFIG.2A, the arrangement of waveguides210and slab layer220allows at least some of the light being propagated in the waveguides210to be coupled into the slab layer220from each of the light coupling portions212through the corresponding light coupling edges222across the gap230.

Although not strictly necessary for practicing the inventive concept, the light distribution device200may comprising a cladding layer in the gap230between the light coupling portion212of each waveguide210and the corresponding light coupling edges222of the slab layer220. The cladding layer may be configured to control the coupling of light between the waveguides210and the slab layer220. By way of example, a cladding layer may be included to enhance the coupling of light such that more light is coupled into the slab layer220. As an alternative to the use of a cladding layer, the gap may be filled with air, or any other suitable gas, or a vacuum may be provided in the gap230.

The light coupled into the slab layer220, from each of the waveguides210, is propagated through the slab layer220towards an interference region226such that an interference pattern is formed by interference of light in the slab layer220. In the light distribution device200, two waveguides210are arranged along each of the three sides of the slab layer120, forming three light beam pairs, one pair from each of the three sides of the slab layer220. By activating two or more pairs, complex interference patterns may be generated.

The light distribution device200may further comprise absorbing elements250. Three absorbing elements250are illustrated inFIG.4being arranged along the boundary225in between the light coupling portions212of the waveguides210. More specifically, the absorbing elements250are arranged such that the light beams in the slab layer220, coupled from the different waveguides210, are incident on an absorbing element250when reaching the boundary225of the slab layer220. The absorbing elements250are made of a light absorbing material that efficiently absorb the light. In this manner, unwanted light reflections from the boundary225may be avoided, which might otherwise reach the interference region226and negatively affect the interference pattern, thereby compromising image quality.

Similarly as to what has been described in relation toFIG.1, the interference pattern generated with light distribution device200may be controlled by a number of influencing devices (not shown) in the path of the light from the light source, prior to entry of the light into the waveguides210. By altering interference pattern, the structured illumination may be changed to illuminate different portions of the sample, and in this manner build up a high-resolution image of the full sample.

As an alternative to the absorption elements250, reflective elements260may be arranged at the same positions along the boundary225. The light distribution device200may be configured to direct light coupled from the waveguides210into the slab layer220, from the light coupling edges222to the reflective element260. The reflective elements260may be configured to reflect at least part of the light back into the slab layer220as reflected light. When the reflected light would reach the interference region226the light and the reflected light may form an interference pattern by interference in the slab layer220. By the present arrangement, an interference pattern may be generated with only a single waveguide210being active. The interference pattern generated by a single light beam being reflected back to the interference region226, may be controlled by an influencing device configured for tuning e.g. a phase, a wavelength, an amplitude, or a polarization of light propagated in the waveguide210. In view of the above it should be realized that a light distribution device200may comprise a plurality of waveguides210but alternatively also a single waveguide210. Hence, it is conceivable that, instead of the light distribution device200comprising six waveguides, the light distribution system200may alternatively comprise a single waveguide210and a reflective element260.

FIG.5illustrates an illumination system400as part of an imaging system500for imaging a sample30. The imaging system500is configured to illuminate the sample30by means of the illumination system400and detect light from the sample30. The illumination system400is herein described as comprising the light distribution device100, however it should be understood that any light distribution device according to the first aspect of the inventive concept, as for example light distribution device200, would be equally applicable as part of the illumination system. The light distribution device100has been described in relation toFIG.1-2, the details of which will not be repeated here.

The illumination system400further comprises a light source410, which in the present example is a laser, configured to generate light. The light source410emits a light beam which is subsequently split up into six light beams, one for each waveguide110in the light distribution device100. Each of the six light beams is guided to an entrance114of a respective waveguide110. The light beams may be guided by a number of input waveguides420, optically connected to the entrance114of the respective waveguides110. Light from the waveguides110is coupled into the slab layer120forming an interference pattern in the interference region126of the slab layer120.

The illumination system400is configured such that the interference pattern formed in the slab layer120has an evanescent light field outside the slab layer120. The evanescent light field is based on a small portion of light escaping a surface of the slab layer120in which total internal reflection occurs and intensity of the light will very quickly decrease with distance from the surface. This evanescent field may interact with the sample30arranged close to the top surface128of the slab layer120and may thus be used for illuminating the sample30selectively illuminating only portions of the sample30very close to the top surface128.

The use of the evanescent field from the slab layer120may thus control a vertical resolution of the sample30being imaged with the imaging system500, since only parts of the sample30very close to the top surface128of the slab layer120will be illuminated. Thus, if the sample30is arranged in close relation to the slab layer120, as for example on the top surface128of the slab layer120above the interference region126, the evanescent light field of the interference pattern may illuminate the sample30. The interference pattern comprises at least one element of constructive interference for selectively illuminating a portion of the sample30.

The illumination system400may further comprise a controller430configured to control forming of the interference pattern in the slab layer120by interference of the light being propagated therein. The controller430is configured to sequentially change the interference pattern in relation to the sample30such that different portions of the sample30are illuminated.

The controller430may send a control signal to the light source410, to control the light emitted by the light source410. Alternatively, the controller430may send control signals to switches at the inputs to the waveguides, such that the inputs are opening and/or closing. By the present arrangement, the controller430may control which of the waveguides110are active waveguides110, thereby controlling the interference pattern in the slab layer120.

The illumination system may comprise a number of influencing devices440, in the present example six influencing devices440. The influencing devices may be connected to the controller430, such that the controller430may send a control signal to each of the respective influencing devices440.

The influencing devices440may be configured for tuning, in response to a signal from the controller430, light being propagated in the respective waveguides110. The influencing devices440may be configured for tuning a phase, a wavelength, an amplitude, or a polarization of the light from the light source410being provided to the waveguides110. Alternatively or additionally, the influencing devices440may be configured for tuning a medium property of the slab layer120and/or the waveguides110, thereby controlling the interference pattern in the slab layer120.

The imaging system500may further comprise a detector510comprising an array512of light sensitive areas514. The detector510may be configured to detect light from the sample30. The detector510may be arranged on a common substrate140with the slab layer120. By way of example, the detector510may be arranged between the slab layer120and the substrate140, or the detector510may be arranged on the opposite side of the substrate140with respect to the slab layer120. Alternatively, the detector510may be arranged on the opposite side of the sample30with respect to the slab layer120, as illustrated inFIG.5.

Each light-sensitive area514is configured to generate a response, such as an electric charge, in proportion to light incident on the light-sensitive area514. Thus, the light-sensitive area514may generate a measurement of intensity of light being emitted by a portion of the sample30. Thanks to the interference pattern used for illuminating the sample30, the light detected by the light sensitive area514may be associated with the illuminated portion of the sample30. Thus, a size of the element of constructive interference of the interference pattern may define the resolution of imaging by the array512of light-sensitive areas514.

The array512of light-sensitive areas514may for example be implemented as a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) image detector. Analog output from the light sensitive areas514may pass an analog-to-digital converter, such that the array512of light-sensitive areas122may output a digital representation of detected light. The digital representation is suited to be transferred to other entities for processing the detected light and/or being processed within the imaging system500.

The detector510may be configured to sequentially detect light from different portions of the sample30, following the sequentially changing of the interference pattern by the controller430. Thus, a plurality of image frames may be acquired in a sequence each of which corresponding to a different interference pattern.

By the present arrangement, interference patterns may be generated having very small elements of constructive interference, thereby providing a very high resolution. By way of example, elements of constructive interference may be generated having a size in the range of 100 nm-10 μm. By sequentially changing the interference pattern, different portions may be illuminated so that light from all portions of the sample30may be sequentially detected. The acquired set of images may be used to reconstruct an image of the full sample30with super-resolution, i.e. resolution of imaging not limited to the free space diffraction limit.

The inventive concept may be applied in e.g. fluorescence microscopy for studying cell and molecular biology, and for nucleic acid sequencing. However, it should be realized that, in addition to fluorescence microscopy, the light distribution device, the illumination system and the imaging system may be applied for various other applications as well. By way of example, they could be used in applications wherein elastically scattered light from the sample is of interest. Moreover, the light distribution device and/or the illumination system may find application also in other fields not related to imaging. Such applications may involve guiding or distributing light in specific manners to manipulate other entities by means of the light. By way of example, the light distribution device and/or the illumination system may find application within the fields of optical trapping and quantum computing.

In the above the inventive concept has mainly been described with reference to a limited number of examples. However, as is readily appreciated by a person skilled in the art, other examples than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.