Description

[0001] This invention relates to an optofluidic , fibre-optic light source with amplified spontaneous emission , intended for use in renewable energy systems and also in other devices / instruments such as biochemical sensors , where cells and materials of biological origin are used as the active medium . Invention relates also to a method for generating light using amplified spontaneous emission . [0002] Optofluidics is a combination of two the fields of science - photonics and microfluidics . This combination creates new opportunities for research and applications , including liquid flow controlled, new optical components ( e . g . optofluidic lenses , liquid tunable resonators ) and new solutions for renewable energy systems . Optofluidic microsystems based on solutions and suspensions of particles allow a st rong and effective interaction with the light beam, particularly with the use of capillaries or l iquid-filled fibres . These special properties are used in biochemical sensors and in the most recent devices inspired by biological systems such as the bio-laser , where cells and materials of biological origin are used as the active medium .

[0003] Interest in optofluidic sensors and in light sources is associated with the development of new types of proteins , mainly for biomedical applications such as cell labelling . The use of optofluidic materials in these instruments is motivated by the fact that such active materials do not exhibit a well-defined discrete structure of energy bands , like the trivalent active dopants Er3+ or Tm3+ in glass , but have a complex band structure , which is the incentive for research on the appropriate design of optofluidic fibre-optic sources .

[0004] Classic fibre-optic light sources operat ing on the basis of amplified spontaneous emission (ASE ) are known . These sources generally have a module consisting of a pumping laser , a collimating system and an optical fibre . In these sources , the optical fibre has an all-glass core doped with rare earth ions . These are convenient sources used in many fields , mainly in telecommunications . The emitted beam is spatially coherent and temporarily incoherent . ASE sources are generally characterised by emission with a spectral width in the order of tens of nanometres . A limitation of thi s type of source is the accessibility of the emission bands in rare earth elements . An example i s published in US5799125 "A Rare Earth Doped Optical Fibre" by Gon zales et al . [0005] ASE sources based on capillary-guided liquids are also known , e . g . from the publication " Silica-based photonic crystal fibre infiltrated with 1 , 2 -dibromoethane for supercontinuum generation" by Hieu Le Van et al . , Applied Optics 16 August 2021 . However , in this case , liquids with a refractive index higher than the refractive index of the material what the capillary is made of are used to ensure light guidance . This , however , limit s their use to specific compounds that can be dissolved in liquids with a high refractive index . At the same time , most biological compounds are naturally dissolved in water , which cannot be used in this case due to its lower refractive index .

[0006] The aim of the invention is to develop a fibre-optic light source with amplified spontaneous emission (ASE ) , based on solutions and suspensions of fluorescent compounds of biological origin , emitting in a spectral range much broader than known fibre-optic sources with glass cores doped with rare earth elements .

[0007 ] A fibre-optic light source with amplified spontaneous emission , comprising a laser module , a microfluidic pump and a fluorescent compound solution according to the invention is featured in that the laser module emitting a beam with a wavelength matched to the fluorescent compound used, and the microfluidic pump feeding, into the core of the anti-resonant fibre ARF a fluorescent compound solution with a refractive index lower than that of the material what the anti-resonant fibre ARF is made of , at a pressure which allows the solution to be fed at a flow rate which ensures reducing the bleaching effect , are connected to the anti-resonant fibre ARF by a reservoir which simultaneously ensures efficient optical coupling between the laser module and the ARF and a tight liquid connection between the microfluidic pump and the anti- resonant fibre ARF .

[0008 ] The wavelength of the light generated by the laser module is preferably larger than or equal to 300 nm, and the anti-resonant fibre ARF is preferably made of glass and/or polymer .

[0009] In a preferable solution the microfluidic pump is capable of feeding the fluorescent solution at pressures in the range of 1 mBar to 1 , 000 mBar , while the core of the fibre-optic is a light guiding core with low loss both for the wavelength of the pumping laser and the fluorescent signal and contains a single layer of internal capillaries or two layers of internal capillaries . Preferably, the core of the ARE is filled with a fluorescent compound solution with a refractive index lower than that of the material what the fibre optic is made of .

[0010 ] The fluorescent compound solut ion is preferably characterised by excitation in the range of 300 to 600 nm and emission in the range of 400 to 800 nm . In a preferable solution , it is Rhodamine 6G, Luciferin , Fluorescein , Coumarin , Stilbene or Umbelif erone .

[0011 ] The reservoir is preferably provided with two channels , wherein the first channel of the reservoir is optically connected to the anti-resonant fibre ARE , and the second channel of the reservoir is in a tight liquid connection with the external microfluidic pump .

[0012 ] A method for generating light using amplified spontaneous emission , wherein a light beam coming from a laser module is interacted with a fibre for the excitation of ampli fied spontaneous emission , according to the invention is featured in that the light beam from the laser module is fed into the core of an anti-resonant fibre ARF filled with a fluorescent compound solution with a refractive index lower than that of the material what the anti- resonant fibre ARF is made of , wherein the core of the fibre-optic is a light guiding core with low loss both for the wavelength of the pumping laser and the fluorescent signal .

[0013] The fluorescent compound solution is preferably fed into the anti-resonant fibre , ARF , under a pressure that allows obtaining a flow rate that ensures the bleaching effect to be reduced, most preferably under a pressure in the range of 1 mBar to 1000 mBar . Preferably, the fluorescent compound solution fed i s characterised by excitation in the range of 300 to 600 nm and emi ssion in the range of 400 to 800 nm, preferably when it is Rhodamine 6G, Luciferin , Fluorescein , Coumarin , Stilbene or Umbel if erone .

[0014 ] The light source and the method according to the invention allow a new and wider range of emitted wavelengths to be obtained by using a new type of fibre . This is possible because both the construction of the source and the steps of the method involve the use of an anti-resonant fibre (ARE) , with its core filled with a solution with a lower refractive index than the material of the fibre, containing a selected fluorescent compound or a mixture of selected compounds. This source allows spontaneous emission amplification over a spectral range much broader than known sources based on rare earth elements. Because, in this case, organic or inorganic fluorescent chemical compounds that cover the visible spectrum are used as active ions, the developed source has all the advantages of classic ASE sources (high spatial coherence and low temporal coherence) and, at the same time, offers emission in a spectral range inaccessible to ASE sources based on dopants of rare earth elements.

[0015] The object of the invention is shown in embodiments with reference to attached a drawing, wherein:

Fig. 1 shows a diagram of an example source,

Fig. 2 shows a cross-section of a fibre:

(a) with a single layer of internal capillaries,

(b) with two layers of internal capillaries,

Fig. 3 shows a cross-section of a fibre filled with a fluorescent compound solution according to the method according to the invention (hatched area) :

(a) with a single layer of internal capillaries,

(b) with two layers of internal capillaries,

Fig. 4. shows the spectral characteristics of anti-resonant fibres :

(a) a fibre with a single layer of internal capillaries, filled with a solution of Rhodamine 6G in water,

(b) a fibre with two layers of internal capillaries, filled with a solution of Rhodamine 6G in a 1:1 solution of water and ethanol ,

Fig. 5. shows the dependence of the luminescence intensity as a function of microfluidic pump pressure when implementing the method according to the invention with a fibre with a single layer of internal capillaries, filled with a solution of Rhodamine 6G in water, while

Fig. 6. shows the fibres with an indication of relevant dimensions .

[0016] The invention will be explained in more detail in embodiments of a fibre-optic light source with amplified spontaneous emission, in which a medium in the form of a solution with a lower refractive index than the material of the fibre flows continuously through the core of the fibre , according to the method according to the invention .

[0017 ] An example source consists of a laser module 2 intended to excite (pump ) a fluorescent compound, an anti-resonant fibre ARE 1 filled with a fluorescent compound solution , and a reservoir 4 tightly connected to a pump 3 and ensuring simultaneous feeding of the solution and introduction of light into the core of the fibre 1 . Efficient coupling of the laser module 2 to the fibre 1 is ensured by the special reservoir 4 which, on the one hand, positions the fibre 1 with respect to the module 2 and, on the other hand, ensures the simultaneous flow of the dye solution through the fibre 1 and the delivery of light from the laser 2 to the core of this fibre . [0018 ] In the embodiment discussed, the reservoir 4 is an aluminium cube with two channels 5 , 6 hollowed out that connect the optical system and the liquid system of the source . One of these, channel 6 , feeds the dye solution and realises a tight connection between the external pump 3 and the ARE 1 and ensures that the solution is delivered continuous ly, at an adjustable pressure in the range of a few mBar to 1 , 000 mBar . In the embodiment discussed, pressures of 100 and 200 mBar were used . After flowing into the channel 6 , the solution flows into the channel 5 and fills the ant i-resonant fibre (ARE ) connected to the reservoir ( glued in ) and pos itioned with a gasket 8 , and then flows out of the other end of this fibre . Through the channel 5 , sealed with a glass window 7 , the access of laser light to the reservoir is ensured and the efficient introduction of light into the anti-resonant fibre 1 and the excitation of fluorescence in the dye are realised . In the embodiment discussed, a typical laser module consisting of a laser ( Coherent Verdi 5W, X=532 nm, power 5W, line width < 5MHz ) was used . Two types of anti- resonant fibre were used . The first variant ( #F1 ) uses a 47 mm long ARF characterised by an outer diameter of D = 125 pm and an inner diameter of d = 80 pm . Inside the fibre , there is a single layer of seven capillaries with a diameter of de = 23 . 5 pm and a thickness of t = 1 . 884 pm . This provides an inner core diameter of dr = 41 . 5 pm .

[0019] The second variant ( #F2 ) uses a 50 mm long fibre ARF characterised by an outer diameter of D = 165 pm and an inner diameter of d = 118 pm. Inside the fibre-optic, there is a double layer of seven capillaries with diameters di = 35 pm (larger capillaries) and da = 20 pm (smaller capillaries) and thicknesses ti = 1.467 pm (larger capillaries) and ta = 0.766 pm (smaller capillaries) . This provides an inner core diameter of dr = 48 pm. As the optically active medium, a fluorescent solution is used in the form of an organic dye used for labelling in biology - Rhodamine 6G. The dye was dissolved in water with a refractive index of 1.33 (first variant #F1) and in a 1:1 mixture of water and ethanol with a refractive index of 1.345 (second variant #F2) . In both cases, there was a dye concentration of -IxlCh ⁴ mol/1.

[0020] Both solutions used have a refractive index lower than the refractive index of glass (for silica glass, n = 1.461 for X = 532 nm) by more than 0.1. This is an important feature of the method according to the invention because the anti-resonant fibre allows light to be guided in the core with a lower refractive index than the fibre cladding, due to the inhibited coupling mechanism.

[0021] ARFs guide light according to an anti-resonance (inhibited coupling) mechanism and are characterised by transmission windows where they exhibit low losses and by areas where losses are very high. Fibre optics provide, on the one hand, a large cross-section to allow efficient flow of the solution and, in addition, ensure that light is guided through a medium with a lower refractive index which allows the light to extend its path of interaction with the active medium.

[0022] Thanks to the use of anti-resonant fibres ARFs, any solutions of organic compounds and molecules that are usually dissolved in water or ethanol, making their refractive index lower than that of the material what the fibre is made of, can be used in ASE sources. The active medium in the example source can also be constituted by other liquids, i.e. chemical dyes, fluorescent proteins and bacteria, including bacteria with modified DNA. These liquids allow the limitation associated with the optical degradation of currently used laser dyes to be overcome. It is therefore possible to almost freely choose the compound and the liquid in which the compound is contained .

[0023] Thus, the source according to the proposed solution can be the basis for developing ASE sources for other spectral lengths in the visible range with other organic dyes , such as , but not limited to :

Luciferin - excitation 470 nm, emission 500-580 nm,

Fluorescein - excitation 480 nm, emission 530-560 nm,

Coumarin - excitation 440 nm, emission 490- 620 nm, Stilbene - excitation 300 nm, emission 410-480 nm, Umbeliferone ( 7-hydroxycoumarin sulphate ) - excitat ion 330 nm, emission 450-490 nm,

[0024 ] With Rhodamine 6G used as the active medium, an ASE-type fibre source was obtained with a spectral half-width of 540 - 618 nm, with continuous characteristics and good optical quality of the beam, and a very low emission half-angle of NA=0 . 04 , which is provided by the anti-resonant fibre , ARE .

[0025] The source generated is characterised by low temporal coherence and high spatial coherence . Commercially available fibreoptic ASE sources made on fibres doped with rare earth elements have similar characteristics . However , in this case , the resulting ARF-based source has similar beam parameters (temporal and spatial coherence ) , but for a wavelength and range inaccessible to any rare earth elements in the silica glass matrix .

[0026] The use , in the source according to the invention , of a fibre with a liquid core with a refractive index lower than that of the glass what the fibre is made of is extremely important when developing the concept of fibre-optic light sources based on organic compounds and living cells , due to the need to keep these compounds in typical solutions based on water , nutrient media or possibly ethanol .

[0027 ] All these media have a refractive index lower than silica glass and cannot be effectively used as a core in fibre optic systems based on the phenomenon of total internal reflection . It was found that filling the core of an anti-resonant fibre with liquids , despite significantly reducing the contrast between the core and the cladding, does not significantly affect the transmission bandwidth . It also positively shifts existing bands towards shorter wavelengths . This allows wide bands to be shifted from the near-infrared to the visible band region , which allows the use of organic dyes in aqueous and ethanol-based solutions .

[0028 ] In addition , the proposed source is an excellent sensor for detecting low concentrations of analytes in biological liquids and the large diameter of the core - of the order of 40-50 microns, compared to fibre cores with a photonic gap (approximately 6-8 microns) , ensures a high speed of sensor filling and flushing. These characteristics - the filling rate and the long interaction path of light with the analyte in aqueous solutions - predispose the proposed source to be used in biochemical sensors.

[0029] Furthermore, when using anti-resonant fibres in ASE sources, it is important that their transmission windows fall within both the pumping laser wavelength and the spontaneous emission wavelength. The wavelength Am for which the highest losses are observed can be determined with the formula: where: n and ni are the refractive indexes of the glass what the fibre (ARE) is made of and the refractive index of the liquid filling this core, respectively, t is the thickness of the internal capillaries, and m defines the boundary of the subsequent transmission window (m= 1, 2, . . . ) .

[0030] Using this dependence, it is possible to determine the positions of areas of high loss according to the capillary thickness of the fibre. The fibre used in the first variant of the embodiment (#F1) , when filled with water-soluble dye, ensures that both excitation (532 nm) and spontaneous emission (maximum for 580 nm) occur in the same transmission window.

[0031] The fibre used in the second variant of the embodiment (#F2) , when using a solvent in the form of a 1:1 mixture of water and ethanol, ensures that excitation occurs in one transmission window and spontaneous emission in another (subsequent) window.

[0032] The above embodiments serve only as an illustration of the inventive idea and in no way constitute a limitation of the scope of patent protection, as defined in the appended patent claims.