Planar waveguide device with nano-sized filter

Abstract

A planar waveguide device (PWD) for interacting with a fluid (FLD) is disclosed, the planar waveguide device (PWD) comprising a waveguide layer (WGL) for supporting optical confinement, a coupling arrangement (CPA) for in-coupling and out-coupling of light into and from the waveguide layer (WGL), a fluid zone (FZN) for accommodating the fluid (FLD), a filter layer (FTL) arranged between the fluid zone (FZN) and the waveguide layer (WGL) in an interaction region (IAR) of the waveguide layer (WGL),
wherein the filter layer (FTL) comprises filter openings (FOP) arranged to allow the fluid (FLD) to interact with an evanescent field of light guided by the waveguide layer (WGL),
wherein the filter openings (FOP) are adapted to prevent particles (PAR) larger than a predefined size from interacting with said evanescent field,
wherein the filter openings (FOP) are arranged as line openings having their longitudinal direction in parallel with the direction of propagation (DOP) of light guided by the waveguide layer (WGL).

Claims

1. A planar waveguide device for interacting with a fluid, the planar waveguide device comprising a waveguide layer for supporting optical confinement, a coupling arrangement for in-coupling and out-coupling of light into and from the waveguide layer, a fluid zone for accommodating the fluid, a filter layer arranged between the fluid zone and the waveguide layer in an interaction region (IAR) of the waveguide layer, wherein the filter layer comprises filter openings arranged to allow the fluid to interact with an evanescent field of light guided by the waveguide layer, wherein the filter openings are adapted to prevent particles larger than a predefined size from interacting with said evanescent field, wherein the filter openings are arranged as line openings having their longitudinal direction in parallel with the direction of propagation of light guided by the waveguide layer, wherein the planar waveguide device further comprises a cladding layer adjacent to the waveguide layer, wherein the cladding layer has a refractive index lower than that of the waveguide layer, and wherein the cladding layer and the filter layer are made from the same material.

2. The planar waveguide device according to claim 1, wherein the filter openings are defined by a line spacing of at most 10 micrometer.

3. The planar waveguide device according to claim 2, wherein the filter openings are defined by a line spacing of at most 5 micrometer, at most 1 micrometer, at most 800 nanometer, at most 200 nanometer, or at most 100 nanometer.

4. The planar waveguide device according to claim 1, wherein said coupling arrangement comprises an in-coupling element for in-coupling of light into the waveguide layer and an out-coupling element for out-coupling of light from the waveguide layer, and wherein the interaction region extends between the in-coupling element and the out-coupling element.

5. The planar waveguide device according to claim 1, wherein said coupling arrangement comprises an in-coupling element for in-coupling of light into the waveguide layer and an out-coupling element for out-coupling of light from the waveguide layer, and wherein the interaction region extends between the in-coupling element and the out-coupling element and also over the out-coupling element.

6. The planar waveguide device according to claim 1, wherein said coupling arrangement extends over at least part of the interaction region.

7. The planar waveguide device according to claim 6, wherein said coupling arrangement extends over the whole of the interaction region.

8. The planar waveguide device according to claim 1, wherein the out-coupling element comprises a dispersive element.

9. The planar waveguide device according to claim 8, wherein the dispersive element is a grating.

10. The planar waveguide device according to claim 1, wherein the planar waveguide device further comprises a laser device as a light source.

11. The planar waveguide device according to claim 1, wherein the planar waveguide device further comprises a broadband light source as a light source.

12. The planar waveguide device according to claim 1, wherein the planar waveguide device further comprises an array based light sensor.

13. The planar waveguide device according to claim 12, wherein the array based light sensor is a CMOS sensor, CCD sensor, or photodiode array sensor.

14. The planar waveguide device according to claim 1, wherein the planar waveguide device further comprises an optical spectrometer as a light sensor.

15. The planar waveguide device according to claim 1, wherein the fluid is a liquid.

16. The planar waveguide device according to claim 1, wherein the planar waveguide device further comprises a fluid flow channel forming the fluid zone.

17. The planar waveguide device according to claim 1, wherein the fluid flow channel is a flow cell.

18. A method of detecting blood hemolysis, the method comprising using a planar waveguide device according to claim 1.

19. A method of interacting light with a fluid, the method comprising coupling light into a waveguide layer, guiding light within the waveguide layer forming an evanescent field outside the waveguide layer, interacting the evanescent field of guided light with the fluid, filtering the fluid so as to prevent particles larger than a predefined size from interacting with said evanescent field using a filter layer comprising filter openings arranged to allow the fluid to interact with an evanescent field of light guided by the waveguide layer, coupling interacted light out from the waveguide layer, wherein the filter openings are arranged as line openings having their longitudinal direction in parallel with the direction of propagation of light guided by the waveguide layer.

20. The method according to claim 19, wherein the method further comprises measuring at least one characteristic of the outcoupled light.

Description

THE FIGURES

(1) The invention will now be described with reference to the figures where

(2) FIG. 1 illustrates a general planar waveguide device according to an embodiment of the invention,

(3) FIGS. 2-4 illustrate cross-section side views of planar waveguide devices according to embodiments of the invention,

(4) FIGS. 5-6 illustrate perspective views of planar waveguide devices according to an embodiments of the invention,

(5) FIG. 7 illustrates a planar waveguide device according to an embodiment of the invention,

(6) FIG. 8 illustrates a planar waveguide device according to an embodiment of the invention,

(7) FIGS. 9A-9D and 10 illustrate experimental data obtained using a planar waveguide device of the invention.

DETAILED DESCRIPTION

(8) Referring to FIG. 1, a schematic view of a planar waveguide device PWD according to an embodiment of the invention is shown. The planar waveguide device PWD is adapted for allowing interaction between a fluid FLD and a light beam LTG. This is done by means of a filter layer FTL, as described in more detail below.

(9) Further embodiments are illustrated in more detail on FIGS. 2-6, and all of these embodiments may be understood in the light of FIG. 1 and the discussion thereof below.

(10) Returning to FIG. 1, the planar waveguide device PWD comprises a waveguide layer WGL for supporting optical confinement, a coupling arrangement CPA, a fluid zone FZN for accommodating the fluid FLD, and a filter layer FTL.

(11) The filter layer FTL is nano-sized in the sense that the width of the filter openings FOP may typically be at most 10 micrometer, such as at most 5 micrometer, such as at most 1 micrometer, such as at most 800 nanometer, such as at most 200 nanometer, such as at most 100 nanometer.

(12) The planar waveguide device PWD may further comprise a light source LSO and a light sensor LSE. The light source LSO emits a light beam LTB, e.g. a laser beam from a laser device or a broadband light beam from a broadband light source.

(13) The coupling arrangement CPA is adapted for in-coupling and out-coupling of light of the light beam into and from the waveguide layer WGL. In FIG. 1, the coupling arrangement CPA comprises a separate in-coupling element ICPA and a separate out-coupling element OCPA; however, in other embodiments the coupling arrangement CPA may be formed by a single coupling element CPA performing both the in-coupling and out-coupling of the light into and from the waveguide layer WGL. The coupling arrangement CPA may comprise a grating, a prism, or a direct coupling to an optical fiber.

(14) The filter layer FTL comprises filter openings FOP arranged to allow the fluid FLD to interact with an evanescent field of light guided by the waveguide layer WGL.

(15) The filter layer FTL is arranged between the fluid zone FZN and the waveguide layer WGL in an interaction region IAR of the waveguide layer WGL. Thereby, the filter openings FOP can prevent particles PAR larger than a predefined size from interacting with said evanescent field. The predefined size is typically determined by the width of the filter openings FOP, which are in the nano-scale region, e.g. at most 10 micrometer. In other words, the filter layer FTL separates the fluid zone FZN from the waveguide layer WGL, in the sense that in controls passage of material between the two. The planar waveguide device PWD may sometimes comprise a further layer between the filter layer FTL and the waveguide layer WGL, e.g. to provide protection of the waveguide layer WGL or to provide selective bonding to e.g. antibodies, polymers, aptamers or other receptors for binding of specimen in the fluid. However, the further layer must be arranged to allow the evanescent field to extend into the fluid.

(16) Further to the above it should be understood that interactions with said evanescent field interactions are in the filter openings FOP. I.e. by allowing the fluid FLD to enter into the filter openings FOP, the fluid FLD is allowed to interact with the evanescent field, and by preventing particles PAR larger than a predefined size from entering the filter openings FOP, the particles PAR are prevented from interacting with said evanescent field.

(17) The filter openings FOP are arranged as line openings having their longitudinal direction in parallel with the direction of propagation DOP of light guided by the waveguide layer WGL. This is illustrated more clearly in some the following figures, e.g. FIGS. 5-6. Thereby, the filter layer FTL is optically decoupled from the waveguide in the sense that the effect by the filter itself on the light guided by the waveguide layer is minimized or practically avoided. Here it should be understood that the line openings having their longitudinal direction parallel with the direction of propagation DOP of light guided by the waveguide layer WGL is during operation of the planar waveguide device PWD when light is guided in the waveguide layer WGL.

(18) Now, referring to FIGS. 2 and 5, a planar waveguide device PWD according to a further embodiment of the invention is illustrated in a cross-sectional side view on FIG. 2 and in a perspective view on FIG. 5.

(19) Further to what is illustrated on FIG. 1, the in-coupling arrangement CPA is here seen as being made up by two coupling elements; an in-coupling element ICPA, and an out-coupling element OCPA.

(20) In FIGS. 2 and 5 the in-coupling element ICPA and the out-coupling element OCPA are both illustrated as gratings. However, in other embodiments the coupling elements may be provided by different means as mentioned with FIG. 1, and need not be the same, e.g. a prism may be used as an in-coupling element ICPA, and a grating may be used as an out-coupling element OCPA.

(21) A light beam LTB is coupled into the waveguide layer WGL by means of the in-coupling element ICPA, then guided through the waveguide layer WGL in the direction of propagation DOP, passing by filter layer FTL in the interaction region IAR to the out-coupling element OCPA, where it is coupled out from the waveguide layer WGL.

(22) Light source LSO and light sensor LSE are not illustrated on FIG. 2 or 5, but may be utilized as in FIG. 1.

(23) As can be seen from both FIGS. 2 and 5, the interaction region IAR defined by the extent of the filter layer FTL extends between the in-coupling element ICPA and the out-coupling element OCPA, but not over any of these. Thus, the embodiment illustrated in FIGS. 2 and 5 is highly suitable for e.g. absorption and excitation interactions between the fluid and the evanescent field in the filter openings FOP. The area where the filter layer FTL does not extend, is covered by an upper cladding layer UCL to facilitate guiding in the waveguide layer WGL. Similarly, a lower cladding layer LCL is positioned below the waveguide layer WGL. Typically, the refractive indices the of the upper and lower cladding layer UCL, LCL are lower than the refractive index of the waveguide layer WGL.

(24) In FIG. 5 the particles PAR not allowed to enter into the filter openings FOP and thus prevented from interacting with the evanescent field therein may represent red blood cells in a blood hemolysis sensor setup. However, they also illustrate the more general principle that particles having a size, e.g. a diameter, larger than a predefined size defined by the width of the filter openings FOP, are prevented from entering the filter openings FOP and interacting with the evanescent field.

(25) It is noted that FIG. 5 is made partly see-through to help understand the composition of the varies elements of the illustrated planar waveguide device PWD.

(26) In FIG. 3 a slightly modified embodiment is illustrated in a cross-sectional side view. Here, the filter layer FTL extends also over the out-coupling element OCPA to allow interaction between the fluid and the evanescent field of the guided light during out-coupling. Since the planar waveguide device PWD illustrated on FIG. 3 has a guided distance along the filter layer FTL (i.e. the in-coupling element ICPA and the out-coupling elements OCPA are separated by some distance) the fluid FLD is allowed to interact with the evanescent field here, making it suitable for absorption and excitation interactions with the fluid. Since the filter layer FTL and this the interaction region IAR extends also over the out-coupling element OCPA, the illustrated planar waveguide device PWD is also suitable for providing information about the refractive index of the fluid FLD.

(27) Now referring to FIGS. 4 and 6, two similar embodiments are illustrated. FIG. 4 illustrates a cross-sectional side view, while FIG. 6 illustrates a perspective view. While FIG. 6 illustrates only the interaction region IAR, FIG. 4 shows also the waveguide layer WGL extending a bit beyond that. In both embodiments, the coupling arrangement CPA is composed by a single coupling element thus providing both in-coupling of light into the waveguide layer WGL and out-coupling therefrom again. Since the out-coupling is performed within the interaction region IAR, the out-coupling is influenced by the refractive index of the fluid FLD, and thus the illustrated planar waveguide devices PWD are suitable for measurement of the refractive index of the fluid FLD.

(28) It is noted that FIG. 6 is made partly see-through to help understand the composition of the varies elements of the illustrated planar waveguide device PWD.

(29) Referring to FIG. 7, a planar waveguide device PWD according to an embodiment of the invention is illustrated. The planar waveguide device PWD comprises a filter layer FTL and waveguide layer WGL, e.g. as described in relation to FIGS. 1 and 5. The fluid zone FZN is formed as a fluid channel extending so as to facilitate a flow of fluid coming into contact with the filter layer FTL. In FIG. 7, the direction of the fluid flow is approximately perpendicular to the direction of propagation of light, whereas in other embodiments the relative angle may be e.g. approximately 45 degrees or 0, i.e. a parallel configuration. In FIG. 7, the fluid to be measured is supplied to the fluid zone FZN and extracted therefrom again by suitable tubes. This illustrates that in the context of FIG. 7, the fluid is provided continuously to the planar waveguide device PWD, preferably by a relatively steady flow rate, in contrast to e.g. a fluid flow dictated by surroundings when using the planar waveguide device PWD submerged in an environmental situation (i.e. not in the laboratory), or when fluid flow is approximately zero.

(30) Referring to FIG. 8, a planar waveguide device PWD according to an embodiment of the invention is illustrated. It is noted that FIG. 8 is made partly see-through to help understand the composition of the varies elements of the illustrated planar waveguide device PWD.

(31) In this embodiment, the planar waveguide device PWD comprises two paths for light, the upper left path being similar to that described in relation to FIGS. 1 and 5, the lower right being identical only that no filter openings are present in the filter layer FTL.

(32) This allows the light to be sent by two substantially identical paths with the difference that light is interacted with a fluid in the upper left path but not in the lower left path.

(33) In one embodiment, the same light source is used for each path, e.g. by utilizing a double slit to split the original light beam into two. After outcoupling of the light beams from each of the two paths, the two outcoupled light beams may be interacted e.g. by interference. This may for example be done using another double slit to create an interference pattern, or by using modified output coupling arrangement, e.g. a modified grating coupler arrangement. By means of this setup, changes in refractive index of the fluid may be measured.

EXAMPLES

(34) A planar waveguide device was excited with a 532 nanometer laser through grating couplers. The image of the fluid zone in the form of a flow channel is captured with a CMOS camera through a microscope objective. A fluorescent emission filter was used in between to eliminate the excitation wavelength. The waveguide device comprises a filter layer according to the invention with a filter opening having a width of 200-220 nanometer and with a 400 nanometer periodicity.

(35) An autofluorescence pattern is generated by the self-fluorescence of the waveguide polymer, where the light is travelling in a direction corresponding to vertically through the image and the fluid flow is perpendicular to the light propagation. The result of the autofluorescence is shown in FIG. 9A.

(36) Two types of polystyrene red fluorescent beads with different diameters (100 nanometer and 2 micrometer) in aqueous suspension were used to characterize the size exclusion function. Both were red fluorescent and used with 0.1% solid concentration. The results are shown in FIG. 9B (2 micrometer beads) and FIG. 9C (100 nanometer beads). Also, the results of FIG. 9A-9C are shown in a comparable manner in FIG. 9D, showing the normalized fluorescence intensity for each of the three measurements as a function of the distance across the waveguide (in micrometers).

(37) These results demonstrated much stronger fluorescent response from the 100 nm beads, i.e. they are excited by the waveguide evanescent field. The 2 um beads can be only excited with scattering light from the waveguide.

(38) Thus, FIGS. 9A-C and corresponding FIG. 9D demonstrate a selective interaction between the planar waveguide device and particles, where particles with a diameter larger than a predefined size are prevented from interacting with the light of the waveguide device.

(39) In FIG. 10, measurements of different hemoglobin (Hb) concentrations in whole blood (WB) and plasma are shown. The photo-spectrometer reference spectra are scaled and plotted at the background. In more detail, FIG. 10 shows the measurements of whole blood samples (middle line) and their plasma counterparts (bottom line) as well as the photo-spectrometer reference measurements with 1 cm cuvettes (upper gray dashed line), where the latter is scaled in amplitude for comparison. The maximum Hb concentration used is 200 mg/dL, which corresponds to about 0.7% hemolysis. Each data point is based on three measurements. At 0 and 100 mg/dL Hb concentrations, the coefficients of variation (CoV) are 1.65% and 0.86%, respectively, showing excellent repeatability of the sensor. On the other hand, comparing the whole blood and plasma measurements, we observed very good overlaps which shows that filtration is highly effective. The absorbance of the WB samples is slightly higher than that of the plasma, which can be attributed to the unspecific scattering of the light which can be absorbed by red blood cells in the bulk.

FIGURE REFERENCES

(40) PWD. Planar waveguide device FLD. Fluid WGL. Waveguide layer CPA. Coupling arrangement FTL. Filter layer ICPA. In-coupling element OCPA. Out-coupling element FZN. Fluid zone IAR. Interaction region FOP. Filter openings PAR. Particles DOP. Direction of propagation LCL. Lower cladding layer UCL. Upper cladding layer LSE. Light sensor LSO. Light source LTB. Light beam